PERLGUTS(1) Perl Programmers Reference Guide PERLGUTS(1)NAMEperlguts - Perl's Internal Functions
DESCRIPTION
This document attempts to describe some of the internal
functions of the Perl executable. It is far from complete
and probably contains many errors. Please refer any
questions or comments to the author below.
Variables
Datatypes
Perl has three typedefs that handle Perl's three main data
types:
SV Scalar Value
AV Array Value
HV Hash Value
Each typedef has specific routines that manipulate the
various data types.
What is an ""IV""?
Perl uses a special typedef IV which is a simple integer
type that is guaranteed to be large enough to hold a
pointer (as well as an integer).
Perl also uses two special typedefs, I32 and I16, which
will always be at least 32-bits and 16-bits long,
respectively.
Working with SVs
An SV can be created and loaded with one command. There
are four types of values that can be loaded: an integer
value (IV), a double (NV), a string, (PV), and another
scalar (SV).
The six routines are:
SV* newSViv(IV);
SV* newSVnv(double);
SV* newSVpv(char*, int);
SV* newSVpvn(char*, int);
SV* newSVpvf(const char*, ...);
SV* newSVsv(SV*);
To change the value of an *already-existing* SV, there are
seven routines:
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void sv_setiv(SV*, IV);
void sv_setuv(SV*, UV);
void sv_setnv(SV*, double);
void sv_setpv(SV*, const char*);
void sv_setpvn(SV*, const char*, int)
void sv_setpvf(SV*, const char*, ...);
void sv_setpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
void sv_setsv(SV*, SV*);
Notice that you can choose to specify the length of the
string to be assigned by using sv_setpvn, newSVpvn, or
newSVpv, or you may allow Perl to calculate the length by
using sv_setpv or by specifying 0 as the second argument
to newSVpv. Be warned, though, that Perl will determine
the string's length by using strlen, which depends on the
string terminating with a NUL character.
The arguments of sv_setpvf are processed like sprintf, and
the formatted output becomes the value.
sv_setpvfn is an analogue of vsprintf, but it allows you
to specify either a pointer to a variable argument list or
the address and length of an array of SVs. The last
argument points to a boolean; on return, if that boolean
is true, then locale-specific information has been used to
format the string, and the string's contents are therefore
untrustworthy (see the perlsec manpage). This pointer may
be NULL if that information is not important. Note that
this function requires you to specify the length of the
format.
The sv_set*() functions are not generic enough to operate
on values that have "magic". See the section on Magic
Virtual Tables later in this document.
All SVs that contain strings should be terminated with a
NUL character. If it is not NUL-terminated there is a
risk of core dumps and corruptions from code which passes
the string to C functions or system calls which expect a
NUL-terminated string. Perl's own functions typically add
a trailing NUL for this reason. Nevertheless, you should
be very careful when you pass a string stored in an SV to
a C function or system call.
To access the actual value that an SV points to, you can
use the macros:
SvIV(SV*)
SvNV(SV*)
SvPV(SV*, STRLEN len)
which will automatically coerce the actual scalar type
into an IV, double, or string.
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In the SvPV macro, the length of the string returned is
placed into the variable len (this is a macro, so you do
not use &len). If you do not care what the length of the
data is, use the global variable PL_na or a local variable
of type STRLEN. However using PL_na can be quite
inefficient because PL_na must be accessed in thread-local
storage in threaded Perl. In any case, remember that Perl
allows arbitrary strings of data that may both contain
NULs and might not be terminated by a NUL.
Also remember that C doesn't allow you to safely say
foo(SvPV(s, len), len);. It might work with your compiler,
but it won't work for everyone. Break this sort of
statement up into separate assignments:
STRLEN len;
char * ptr;
ptr = SvPV(len);
foo(ptr, len);
If you want to know if the scalar value is TRUE, you can
use:
SvTRUE(SV*)
Although Perl will automatically grow strings for you, if
you need to force Perl to allocate more memory for your
SV, you can use the macro
SvGROW(SV*, STRLEN newlen)
which will determine if more memory needs to be allocated.
If so, it will call the function sv_grow. Note that
SvGROW can only increase, not decrease, the allocated
memory of an SV and that it does not automatically add a
byte for the a trailing NUL (perl's own string functions
typically do SvGROW(sv, len + 1)).
If you have an SV and want to know what kind of data Perl
thinks is stored in it, you can use the following macros
to check the type of SV you have.
SvIOK(SV*)
SvNOK(SV*)
SvPOK(SV*)
You can get and set the current length of the string
stored in an SV with the following macros:
SvCUR(SV*)
SvCUR_set(SV*, I32 val)
You can also get a pointer to the end of the string stored
in the SV with the macro:
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SvEND(SV*)
But note that these last three macros are valid only if
SvPOK() is true.
If you want to append something to the end of string
stored in an SV*, you can use the following functions:
void sv_catpv(SV*, char*);
void sv_catpvn(SV*, char*, STRLEN);
void sv_catpvf(SV*, const char*, ...);
void sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
void sv_catsv(SV*, SV*);
The first function calculates the length of the string to
be appended by using strlen. In the second, you specify
the length of the string yourself. The third function
processes its arguments like sprintf and appends the
formatted output. The fourth function works like
vsprintf. You can specify the address and length of an
array of SVs instead of the va_list argument. The fifth
function extends the string stored in the first SV with
the string stored in the second SV. It also forces the
second SV to be interpreted as a string.
The sv_cat*() functions are not generic enough to operate
on values that have "magic". See the section on Magic
Virtual Tables later in this document.
If you know the name of a scalar variable, you can get a
pointer to its SV by using the following:
SV* perl_get_sv("package::varname", FALSE);
This returns NULL if the variable does not exist.
If you want to know if this variable (or any other SV) is
actually defined, you can call:
SvOK(SV*)
The scalar undef value is stored in an SV instance called
PL_sv_undef. Its address can be used whenever an SV* is
needed.
There are also the two values PL_sv_yes and PL_sv_no,
which contain Boolean TRUE and FALSE values, respectively.
Like PL_sv_undef, their addresses can be used whenever an
SV* is needed.
Do not be fooled into thinking that (SV *) 0 is the same
as &PL_sv_undef. Take this code:
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SV* sv = (SV*) 0;
if (I-am-to-return-a-real-value) {
sv = sv_2mortal(newSViv(42));
}
sv_setsv(ST(0), sv);
This code tries to return a new SV (which contains the
value 42) if it should return a real value, or undef
otherwise. Instead it has returned a NULL pointer which,
somewhere down the line, will cause a segmentation
violation, bus error, or just weird results. Change the
zero to &PL_sv_undef in the first line and all will be
well.
To free an SV that you've created, call SvREFCNT_dec(SV*).
Normally this call is not necessary (see the section on
Reference Counts and Mortality).
What's Really Stored in an SV?
Recall that the usual method of determining the type of
scalar you have is to use Sv*OK macros. Because a scalar
can be both a number and a string, usually these macros
will always return TRUE and calling the Sv*V macros will
do the appropriate conversion of string to integer/double
or integer/double to string.
If you really need to know if you have an integer, double,
or string pointer in an SV, you can use the following
three macros instead:
SvIOKp(SV*)
SvNOKp(SV*)
SvPOKp(SV*)
These will tell you if you truly have an integer, double,
or string pointer stored in your SV. The "p" stands for
private.
In general, though, it's best to use the Sv*V macros.
Working with AVs
There are two ways to create and load an AV. The first
method creates an empty AV:
AV* newAV();
The second method both creates the AV and initially
populates it with SVs:
AV* av_make(I32 num, SV **ptr);
The second argument points to an array containing num
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SV*'s. Once the AV has been created, the SVs can be
destroyed, if so desired.
Once the AV has been created, the following operations are
possible on AVs:
void av_push(AV*, SV*);
SV* av_pop(AV*);
SV* av_shift(AV*);
void av_unshift(AV*, I32 num);
These should be familiar operations, with the exception of
av_unshift. This routine adds num elements at the front
of the array with the undef value. You must then use
av_store (described below) to assign values to these new
elements.
Here are some other functions:
I32 av_len(AV*);
SV** av_fetch(AV*, I32 key, I32 lval);
SV** av_store(AV*, I32 key, SV* val);
The av_len function returns the highest index value in
array (just like $#array in Perl). If the array is empty,
-1 is returned. The av_fetch function returns the value
at index key, but if lval is non-zero, then av_fetch will
store an undef value at that index. The av_store function
stores the value val at index key, and does not increment
the reference count of val. Thus the caller is
responsible for taking care of that, and if av_store
returns NULL, the caller will have to decrement the
reference count to avoid a memory leak. Note that
av_fetch and av_store both return SV**'s, not SV*'s as
their return value.
void av_clear(AV*);
void av_undef(AV*);
void av_extend(AV*, I32 key);
The av_clear function deletes all the elements in the AV*
array, but does not actually delete the array itself. The
av_undef function will delete all the elements in the
array plus the array itself. The av_extend function
extends the array so that it contains at least key+1
elements. If key+1 is less than the currently allocated
length of the array, then nothing is done.
If you know the name of an array variable, you can get a
pointer to its AV by using the following:
AV* perl_get_av("package::varname", FALSE);
This returns NULL if the variable does not exist.
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See the section on Understanding the Magic of Tied Hashes
and Arrays for more information on how to use the array
access functions on tied arrays.
Working with HVs
To create an HV, you use the following routine:
HV* newHV();
Once the HV has been created, the following operations are
possible on HVs:
SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
The klen parameter is the length of the key being passed
in (Note that you cannot pass 0 in as a value of klen to
tell Perl to measure the length of the key). The val
argument contains the SV pointer to the scalar being
stored, and hash is the precomputed hash value (zero if
you want hv_store to calculate it for you). The lval
parameter indicates whether this fetch is actually a part
of a store operation, in which case a new undefined value
will be added to the HV with the supplied key and hv_fetch
will return as if the value had already existed.
Remember that hv_store and hv_fetch return SV**'s and not
just SV*. To access the scalar value, you must first
dereference the return value. However, you should check
to make sure that the return value is not NULL before
dereferencing it.
These two functions check if a hash table entry exists,
and deletes it.
bool hv_exists(HV*, char* key, U32 klen);
SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
If flags does not include the G_DISCARD flag then
hv_delete will create and return a mortal copy of the
deleted value.
And more miscellaneous functions:
void hv_clear(HV*);
void hv_undef(HV*);
Like their AV counterparts, hv_clear deletes all the
entries in the hash table but does not actually delete the
hash table. The hv_undef deletes both the entries and the
hash table itself.
Perl keeps the actual data in linked list of structures
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with a typedef of HE. These contain the actual key and
value pointers (plus extra administrative overhead). The
key is a string pointer; the value is an SV*. However,
once you have an HE*, to get the actual key and value, use
the routines specified below.
I32 hv_iterinit(HV*);
/* Prepares starting point to traverse hash table */
HE* hv_iternext(HV*);
/* Get the next entry, and return a pointer to a
structure that has both the key and value */
char* hv_iterkey(HE* entry, I32* retlen);
/* Get the key from an HE structure and also return
the length of the key string */
SV* hv_iterval(HV*, HE* entry);
/* Return a SV pointer to the value of the HE
structure */
SV* hv_iternextsv(HV*, char** key, I32* retlen);
/* This convenience routine combines hv_iternext,
hv_iterkey, and hv_iterval. The key and retlen
arguments are return values for the key and its
length. The value is returned in the SV* argument */
If you know the name of a hash variable, you can get a
pointer to its HV by using the following:
HV* perl_get_hv("package::varname", FALSE);
This returns NULL if the variable does not exist.
The hash algorithm is defined in the PERL_HASH(hash, key,
klen) macro:
hash = 0;
while (klen--)
hash = (hash * 33) + *key++;
See the section on Understanding the Magic of Tied Hashes
and Arrays for more information on how to use the hash
access functions on tied hashes.
Hash API Extensions
Beginning with version 5.004, the following functions are
also supported:
HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
bool hv_exists_ent (HV* tb, SV* key, U32 hash);
SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
SV* hv_iterkeysv (HE* entry);
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Note that these functions take SV* keys, which simplifies
writing of extension code that deals with hash structures.
These functions also allow passing of SV* keys to tie
functions without forcing you to stringify the keys
(unlike the previous set of functions).
They also return and accept whole hash entries (HE*),
making their use more efficient (since the hash number for
a particular string doesn't have to be recomputed every
time). See the section on API LISTING later in this
document for detailed descriptions.
The following macros must always be used to access the
contents of hash entries. Note that the arguments to
these macros must be simple variables, since they may get
evaluated more than once. See the section on API LISTING
later in this document for detailed descriptions of these
macros.
HePV(HE* he, STRLEN len)
HeVAL(HE* he)
HeHASH(HE* he)
HeSVKEY(HE* he)
HeSVKEY_force(HE* he)
HeSVKEY_set(HE* he, SV* sv)
These two lower level macros are defined, but must only be
used when dealing with keys that are not SV*s:
HeKEY(HE* he)
HeKLEN(HE* he)
Note that both hv_store and hv_store_ent do not increment
the reference count of the stored val, which is the
caller's responsibility. If these functions return a NULL
value, the caller will usually have to decrement the
reference count of val to avoid a memory leak.
References
References are a special type of scalar that point to
other data types (including references).
To create a reference, use either of the following
functions:
SV* newRV_inc((SV*) thing);
SV* newRV_noinc((SV*) thing);
The thing argument can be any of an SV*, AV*, or HV*. The
functions are identical except that newRV_inc increments
the reference count of the thing, while newRV_noinc does
not. For historical reasons, newRV is a synonym for
newRV_inc.
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Once you have a reference, you can use the following macro
to dereference the reference:
SvRV(SV*)
then call the appropriate routines, casting the returned
SV* to either an AV* or HV*, if required.
To determine if an SV is a reference, you can use the
following macro:
SvROK(SV*)
To discover what type of value the reference refers to,
use the following macro and then check the return value.
SvTYPE(SvRV(SV*))
The most useful types that will be returned are:
SVt_IV Scalar
SVt_NV Scalar
SVt_PV Scalar
SVt_RV Scalar
SVt_PVAV Array
SVt_PVHV Hash
SVt_PVCV Code
SVt_PVGV Glob (possible a file handle)
SVt_PVMG Blessed or Magical Scalar
See the sv.h header file for more details.
Blessed References and Class Objects
References are also used to support object-oriented
programming. In the OO lexicon, an object is simply a
reference that has been blessed into a package (or class).
Once blessed, the programmer may now use the reference to
access the various methods in the class.
A reference can be blessed into a package with the
following function:
SV* sv_bless(SV* sv, HV* stash);
The sv argument must be a reference. The stash argument
specifies which class the reference will belong to. See
the section on Stashes and Globs for information on
converting class names into stashes.
/* Still under construction */
Upgrades rv to reference if not already one. Creates new
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SV for rv to point to. If classname is non-null, the SV
is blessed into the specified class. SV is returned.
SV* newSVrv(SV* rv, char* classname);
Copies integer or double into an SV whose reference is rv.
SV is blessed if classname is non-null.
SV* sv_setref_iv(SV* rv, char* classname, IV iv);
SV* sv_setref_nv(SV* rv, char* classname, NV iv);
Copies the pointer value (the address, not the string!)
into an SV whose reference is rv. SV is blessed if
classname is non-null.
SV* sv_setref_pv(SV* rv, char* classname, PV iv);
Copies string into an SV whose reference is rv. Set
length to 0 to let Perl calculate the string length. SV
is blessed if classname is non-null.
SV* sv_setref_pvn(SV* rv, char* classname, PV iv, STRLEN length);
Tests whether the SV is blessed into the specified class.
It does not check inheritance relationships.
int sv_isa(SV* sv, char* name);
Tests whether the SV is a reference to a blessed object.
int sv_isobject(SV* sv);
Tests whether the SV is derived from the specified class.
SV can be either a reference to a blessed object or a
string containing a class name. This is the function
implementing the UNIVERSAL::isa functionality.
bool sv_derived_from(SV* sv, char* name);
To check if you've got an object derived from a specific
class you have to write:
if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }
Creating New Variables
To create a new Perl variable with an undef value which
can be accessed from your Perl script, use the following
routines, depending on the variable type.
SV* perl_get_sv("package::varname", TRUE);
AV* perl_get_av("package::varname", TRUE);
HV* perl_get_hv("package::varname", TRUE);
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Notice the use of TRUE as the second parameter. The new
variable can now be set, using the routines appropriate to
the data type.
There are additional macros whose values may be bitwise
OR'ed with the TRUE argument to enable certain extra
features. Those bits are:
GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
"Name <varname> used only once: possible typo" warning.
GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
the variable did not exist before the function was called.
If you do not specify a package name, the variable is
created in the current package.
Reference Counts and Mortality
Perl uses an reference count-driven garbage collection
mechanism. SVs, AVs, or HVs (xV for short in the
following) start their life with a reference count of 1.
If the reference count of an xV ever drops to 0, then it
will be destroyed and its memory made available for reuse.
This normally doesn't happen at the Perl level unless a
variable is undef'ed or the last variable holding a
reference to it is changed or overwritten. At the
internal level, however, reference counts can be
manipulated with the following macros:
int SvREFCNT(SV* sv);
SV* SvREFCNT_inc(SV* sv);
void SvREFCNT_dec(SV* sv);
However, there is one other function which manipulates the
reference count of its argument. The newRV_inc function,
you will recall, creates a reference to the specified
argument. As a side effect, it increments the argument's
reference count. If this is not what you want, use
newRV_noinc instead.
For example, imagine you want to return a reference from
an XSUB function. Inside the XSUB routine, you create an
SV which initially has a reference count of one. Then you
call newRV_inc, passing it the just-created SV. This
returns the reference as a new SV, but the reference count
of the SV you passed to newRV_inc has been incremented to
two. Now you return the reference from the XSUB routine
and forget about the SV. But Perl hasn't! Whenever the
returned reference is destroyed, the reference count of
the original SV is decreased to one and nothing happens.
The SV will hang around without any way to access it until
Perl itself terminates. This is a memory leak.
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The correct procedure, then, is to use newRV_noinc instead
of newRV_inc. Then, if and when the last reference is
destroyed, the reference count of the SV will go to zero
and it will be destroyed, stopping any memory leak.
There are some convenience functions available that can
help with the destruction of xVs. These functions
introduce the concept of "mortality". An xV that is
mortal has had its reference count marked to be
decremented, but not actually decremented, until "a short
time later". Generally the term "short time later" means
a single Perl statement, such as a call to an XSUB
function. The actual determinant for when mortal xVs have
their reference count decremented depends on two macros,
SAVETMPS and FREETMPS. See the perlcall manpage and the
perlxs manpage for more details on these macros.
"Mortalization" then is at its simplest a deferred
SvREFCNT_dec. However, if you mortalize a variable twice,
the reference count will later be decremented twice.
You should be careful about creating mortal variables.
Strange things can happen if you make the same value
mortal within multiple contexts, or if you make a variable
mortal multiple times.
To create a mortal variable, use the functions:
SV* sv_newmortal()
SV* sv_2mortal(SV*)
SV* sv_mortalcopy(SV*)
The first call creates a mortal SV, the second converts an
existing SV to a mortal SV (and thus defers a call to
SvREFCNT_dec), and the third creates a mortal copy of an
existing SV.
The mortal routines are not just for SVs -- AVs and HVs
can be made mortal by passing their address (type-casted
to SV*) to the sv_2mortal or sv_mortalcopy routines.
Stashes and Globs
A "stash" is a hash that contains all of the different
objects that are contained within a package. Each key of
the stash is a symbol name (shared by all the different
types of objects that have the same name), and each value
in the hash table is a GV (Glob Value). This GV in turn
contains references to the various objects of that name,
including (but not limited to) the following:
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Scalar Value
Array Value
Hash Value
I/O Handle
Format
Subroutine
There is a single stash called "PL_defstash" that holds
the items that exist in the "main" package. To get at the
items in other packages, append the string "::" to the
package name. The items in the "Foo" package are in the
stash "Foo::" in PL_defstash. The items in the "Bar::Baz"
package are in the stash "Baz::" in "Bar::"'s stash.
To get the stash pointer for a particular package, use the
function:
HV* gv_stashpv(char* name, I32 create)
HV* gv_stashsv(SV*, I32 create)
The first function takes a literal string, the second uses
the string stored in the SV. Remember that a stash is
just a hash table, so you get back an HV*. The create
flag will create a new package if it is set.
The name that gv_stash*v wants is the name of the package
whose symbol table you want. The default package is
called main. If you have multiply nested packages, pass
their names to gv_stash*v, separated by :: as in the Perl
language itself.
Alternately, if you have an SV that is a blessed
reference, you can find out the stash pointer by using:
HV* SvSTASH(SvRV(SV*));
then use the following to get the package name itself:
char* HvNAME(HV* stash);
If you need to bless or re-bless an object you can use the
following function:
SV* sv_bless(SV*, HV* stash)
where the first argument, an SV*, must be a reference, and
the second argument is a stash. The returned SV* can now
be used in the same way as any other SV.
For more information on references and blessings, consult
the perlref manpage.
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Double-Typed SVs
Scalar variables normally contain only one type of value,
an integer, double, pointer, or reference. Perl will
automatically convert the actual scalar data from the
stored type into the requested type.
Some scalar variables contain more than one type of scalar
data. For example, the variable $! contains either the
numeric value of errno or its string equivalent from
either strerror or sys_errlist[].
To force multiple data values into an SV, you must do two
things: use the sv_set*v routines to add the additional
scalar type, then set a flag so that Perl will believe it
contains more than one type of data. The four macros to
set the flags are:
SvIOK_on
SvNOK_on
SvPOK_on
SvROK_on
The particular macro you must use depends on which
sv_set*v routine you called first. This is because every
sv_set*v routine turns on only the bit for the particular
type of data being set, and turns off all the rest.
For example, to create a new Perl variable called
"dberror" that contains both the numeric and descriptive
string error values, you could use the following code:
extern int dberror;
extern char *dberror_list;
SV* sv = perl_get_sv("dberror", TRUE);
sv_setiv(sv, (IV) dberror);
sv_setpv(sv, dberror_list[dberror]);
SvIOK_on(sv);
If the order of sv_setiv and sv_setpv had been reversed,
then the macro SvPOK_on would need to be called instead of
SvIOK_on.
Magic Variables
[This section still under construction. Ignore everything
here. Post no bills. Everything not permitted is
forbidden.]
Any SV may be magical, that is, it has special features
that a normal SV does not have. These features are stored
in the SV structure in a linked list of struct magic's,
typedef'ed to MAGIC.
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struct magic {
MAGIC* mg_moremagic;
MGVTBL* mg_virtual;
U16 mg_private;
char mg_type;
U8 mg_flags;
SV* mg_obj;
char* mg_ptr;
I32 mg_len;
};
Note this is current as of patchlevel 0, and could change
at any time.
Assigning Magic
Perl adds magic to an SV using the sv_magic function:
void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
The sv argument is a pointer to the SV that is to acquire
a new magical feature.
If sv is not already magical, Perl uses the SvUPGRADE
macro to set the SVt_PVMG flag for the sv. Perl then
continues by adding it to the beginning of the linked list
of magical features. Any prior entry of the same type of
magic is deleted. Note that this can be overridden, and
multiple instances of the same type of magic can be
associated with an SV.
The name and namlen arguments are used to associate a
string with the magic, typically the name of a variable.
namlen is stored in the mg_len field and if name is non-
null and namlen >= 0 a malloc'd copy of the name is stored
in mg_ptr field.
The sv_magic function uses how to determine which, if any,
predefined "Magic Virtual Table" should be assigned to the
mg_virtual field. See the "Magic Virtual Table" section
below. The how argument is also stored in the mg_type
field.
The obj argument is stored in the mg_obj field of the
MAGIC structure. If it is not the same as the sv
argument, the reference count of the obj object is
incremented. If it is the same, or if the how argument is
"#", or if it is a NULL pointer, then obj is merely
stored, without the reference count being incremented.
There is also a function to add magic to an HV:
void hv_magic(HV *hv, GV *gv, int how);
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This simply calls sv_magic and coerces the gv argument
into an SV.
To remove the magic from an SV, call the function
sv_unmagic:
void sv_unmagic(SV *sv, int type);
The type argument should be equal to the how value when
the SV was initially made magical.
Magic Virtual Tables
The mg_virtual field in the MAGIC structure is a pointer
to a MGVTBL, which is a structure of function pointers and
stands for "Magic Virtual Table" to handle the various
operations that might be applied to that variable.
The MGVTBL has five pointers to the following routine
types:
int (*svt_get)(SV* sv, MAGIC* mg);
int (*svt_set)(SV* sv, MAGIC* mg);
U32 (*svt_len)(SV* sv, MAGIC* mg);
int (*svt_clear)(SV* sv, MAGIC* mg);
int (*svt_free)(SV* sv, MAGIC* mg);
This MGVTBL structure is set at compile-time in perl.h and
there are currently 19 types (or 21 with overloading
turned on). These different structures contain pointers
to various routines that perform additional actions
depending on which function is being called.
Function pointer Action taken
----------------------------
svt_get Do something after the value of the SV is retrieved.
svt_set Do something after the SV is assigned a value.
svt_len Report on the SV's length.
svt_clear Clear something the SV represents.
svt_free Free any extra storage associated with the SV.
For instance, the MGVTBL structure called vtbl_sv (which
corresponds to an mg_type of '\0') contains:
{ magic_get, magic_set, magic_len, 0, 0 }
Thus, when an SV is determined to be magical and of type
'\0', if a get operation is being performed, the routine
magic_get is called. All the various routines for the
various magical types begin with magic_.
The current kinds of Magic Virtual Tables are:
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mg_type MGVTBL Type of magic
-----------------------------------------
\0 vtbl_sv Special scalar variable
A vtbl_amagic %OVERLOAD hash
a vtbl_amagicelem %OVERLOAD hash element
c (none) Holds overload table (AMT) on stash
B vtbl_bm Boyer-Moore (fast string search)
E vtbl_env %ENV hash
e vtbl_envelem %ENV hash element
f vtbl_fm Formline ('compiled' format)
g vtbl_mglob m//g target / study()ed string
I vtbl_isa @ISA array
i vtbl_isaelem @ISA array element
k vtbl_nkeys scalar(keys()) lvalue
L (none) Debugger %_<filename
l vtbl_dbline Debugger %_<filename element
o vtbl_collxfrm Locale transformation
P vtbl_pack Tied array or hash
p vtbl_packelem Tied array or hash element
q vtbl_packelem Tied scalar or handle
S vtbl_sig %SIG hash
s vtbl_sigelem %SIG hash element
t vtbl_taint Taintedness
U vtbl_uvar Available for use by extensions
v vtbl_vec vec() lvalue
x vtbl_substr substr() lvalue
y vtbl_defelem Shadow "foreach" iterator variable /
smart parameter vivification
* vtbl_glob GV (typeglob)
# vtbl_arylen Array length ($#ary)
. vtbl_pos pos() lvalue
~ (none) Available for use by extensions
When an uppercase and lowercase letter both exist in the
table, then the uppercase letter is used to represent some
kind of composite type (a list or a hash), and the
lowercase letter is used to represent an element of that
composite type.
The '~' and 'U' magic types are defined specifically for
use by extensions and will not be used by perl itself.
Extensions can use '~' magic to 'attach' private
information to variables (typically objects). This is
especially useful because there is no way for normal perl
code to corrupt this private information (unlike using
extra elements of a hash object).
Similarly, 'U' magic can be used much like tie() to call a
C function any time a scalar's value is used or changed.
The MAGIC's mg_ptr field points to a ufuncs structure:
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struct ufuncs {
I32 (*uf_val)(IV, SV*);
I32 (*uf_set)(IV, SV*);
IV uf_index;
};
When the SV is read from or written to, the uf_val or
uf_set function will be called with uf_index as the first
arg and a pointer to the SV as the second. A simple
example of how to add 'U' magic is shown below. Note that
the ufuncs structure is copied by sv_magic, so you can
safely allocate it on the stack.
void
Umagic(sv)
SV *sv;
PREINIT:
struct ufuncs uf;
CODE:
uf.uf_val = &my_get_fn;
uf.uf_set = &my_set_fn;
uf.uf_index = 0;
sv_magic(sv, 0, 'U', (char*)&uf, sizeof(uf));
Note that because multiple extensions may be using '~' or
'U' magic, it is important for extensions to take extra
care to avoid conflict. Typically only using the magic on
objects blessed into the same class as the extension is
sufficient. For '~' magic, it may also be appropriate to
add an I32 'signature' at the top of the private data area
and check that.
Also note that the sv_set*() and sv_cat*() functions
described earlier do not invoke 'set' magic on their
targets. This must be done by the user either by calling
the SvSETMAGIC() macro after calling these functions, or
by using one of the sv_set*_mg() or sv_cat*_mg()
functions. Similarly, generic C code must call the
SvGETMAGIC() macro to invoke any 'get' magic if they use
an SV obtained from external sources in functions that
don't handle magic. the section on API LISTING later in
this document identifies such functions. For example,
calls to the sv_cat*() functions typically need to be
followed by SvSETMAGIC(), but they don't need a prior
SvGETMAGIC() since their implementation handles 'get'
magic.
Finding Magic
MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
This routine returns a pointer to the MAGIC structure
stored in the SV. If the SV does not have that magical
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feature, NULL is returned. Also, if the SV is not of type
SVt_PVMG, Perl may core dump.
int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
This routine checks to see what types of magic sv has. If
the mg_type field is an uppercase letter, then the mg_obj
is copied to nsv, but the mg_type field is changed to be
the lowercase letter.
Understanding the Magic of Tied Hashes and Arrays
Tied hashes and arrays are magical beasts of the 'P' magic
type.
WARNING: As of the 5.004 release, proper usage of the
array and hash access functions requires understanding a
few caveats. Some of these caveats are actually
considered bugs in the API, to be fixed in later releases,
and are bracketed with [MAYCHANGE] below. If you find
yourself actually applying such information in this
section, be aware that the behavior may change in the
future, umm, without warning.
The perl tie function associates a variable with an object
that implements the various GET, SET etc methods. To
perform the equivalent of the perl tie function from an
XSUB, you must mimic this behaviour. The code below
carries out the necessary steps - firstly it creates a new
hash, and then creates a second hash which it blesses into
the class which will implement the tie methods. Lastly it
ties the two hashes together, and returns a reference to
the new tied hash. Note that the code below does NOT call
the TIEHASH method in the MyTie class - see the section on
Calling Perl Routines from within C Programs for details
on how to do this.
SV*
mytie()
PREINIT:
HV *hash;
HV *stash;
SV *tie;
CODE:
hash = newHV();
tie = newRV_noinc((SV*)newHV());
stash = gv_stashpv("MyTie", TRUE);
sv_bless(tie, stash);
hv_magic(hash, tie, 'P');
RETVAL = newRV_noinc(hash);
OUTPUT:
RETVAL
The av_store function, when given a tied array argument,
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merely copies the magic of the array onto the value to be
"stored", using mg_copy. It may also return NULL,
indicating that the value did not actually need to be
stored in the array. [MAYCHANGE] After a call to av_store
on a tied array, the caller will usually need to call
mg_set(val) to actually invoke the perl level "STORE"
method on the TIEARRAY object. If av_store did return
NULL, a call to SvREFCNT_dec(val) will also be usually
necessary to avoid a memory leak. [/MAYCHANGE]
The previous paragraph is applicable verbatim to tied hash
access using the hv_store and hv_store_ent functions as
well.
av_fetch and the corresponding hash functions hv_fetch and
hv_fetch_ent actually return an undefined mortal value
whose magic has been initialized using mg_copy. Note the
value so returned does not need to be deallocated, as it
is already mortal. [MAYCHANGE] But you will need to call
mg_get() on the returned value in order to actually invoke
the perl level "FETCH" method on the underlying TIE
object. Similarly, you may also call mg_set() on the
return value after possibly assigning a suitable value to
it using sv_setsv, which will invoke the "STORE" method
on the TIE object. [/MAYCHANGE]
[MAYCHANGE] In other words, the array or hash fetch/store
functions don't really fetch and store actual values in
the case of tied arrays and hashes. They merely call
mg_copy to attach magic to the values that were meant to
be "stored" or "fetched". Later calls to mg_get and
mg_set actually do the job of invoking the TIE methods on
the underlying objects. Thus the magic mechanism
currently implements a kind of lazy access to arrays and
hashes.
Currently (as of perl version 5.004), use of the hash and
array access functions requires the user to be aware of
whether they are operating on "normal" hashes and arrays,
or on their tied variants. The API may be changed to
provide more transparent access to both tied and normal
data types in future versions. [/MAYCHANGE]
You would do well to understand that the TIEARRAY and
TIEHASH interfaces are mere sugar to invoke some perl
method calls while using the uniform hash and array
syntax. The use of this sugar imposes some overhead
(typically about two to four extra opcodes per FETCH/STORE
operation, in addition to the creation of all the mortal
variables required to invoke the methods). This overhead
will be comparatively small if the TIE methods are
themselves substantial, but if they are only a few
statements long, the overhead will not be insignificant.
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Localizing changes
Perl has a very handy construction
{
local $var = 2;
...
}
This construction is approximately equivalent to
{
my $oldvar = $var;
$var = 2;
...
$var = $oldvar;
}
The biggest difference is that the first construction
would reinstate the initial value of $var, irrespective of
how control exits the block: goto, return, die/eval etc.
It is a little bit more efficient as well.
There is a way to achieve a similar task from C via Perl
API: create a pseudo-block, and arrange for some changes
to be automatically undone at the end of it, either
explicit, or via a non-local exit (via die()). A
block-like construct is created by a pair of ENTER/LEAVE
macros (see the section on Returning a Scalar in the
perlcall manpage). Such a construct may be created
specially for some important localized task, or an
existing one (like boundaries of enclosing Perl
subroutine/block, or an existing pair for freeing TMPs)
may be used. (In the second case the overhead of
additional localization must be almost negligible.) Note
that any XSUB is automatically enclosed in an ENTER/LEAVE
pair.
Inside such a pseudo-block the following service is
available:
SAVEINT(int i)
SAVEIV(IV i)
SAVEI32(I32 i)
SAVELONG(long i)
These macros arrange things to restore the value of
integer variable i at the end of enclosing pseudo-
block.
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These macros arrange things to restore the value of
pointers s and p. s must be a pointer of a type which
survives conversion to SV* and back, p should be able
to survive conversion to char* and back.
SAVEFREESV(SV *sv)
The refcount of sv would be decremented at the end of
pseudo-block. This is similar to sv_2mortal, which
should (?) be used instead.
SAVEFREEOP(OP *op)
The OP * is op_free()ed at the end of pseudo-block.
SAVEFREEPV(p)
The chunk of memory which is pointed to by p is
Safefree()ed at the end of pseudo-block.
SAVECLEARSV(SV *sv)
Clears a slot in the current scratchpad which
corresponds to sv at the end of pseudo-block.
SAVEDELETE(HV *hv, char *key, I32 length)
The key key of hv is deleted at the end of pseudo-
block. The string pointed to by key is Safefree()ed.
If one has a key in short-lived storage, the
corresponding string may be reallocated like this:
SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf));
SAVEDESTRUCTOR(f,p)
At the end of pseudo-block the function f is called
with the only argument (of type void*) p.
SAVESTACK_POS()
The current offset on the Perl internal stack (cf.
SP) is restored at the end of pseudo-block.
The following API list contains functions, thus one needs
to provide pointers to the modifiable data explicitly
(either C pointers, or Perlish GV *s). Where the above
macros take int, a similar function takes int *.
SV* save_scalar(GV *gv)
Equivalent to Perl code local $gv.
AV* save_ary(GV *gv)
HV* save_hash(GV *gv)
Similar to save_scalar, but localize @gv and %gv.
void save_item(SV *item)
Duplicates the current value of SV, on the exit from
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the current ENTER/LEAVE pseudo-block will restore the
value of SV using the stored value.
void save_list(SV **sarg, I32 maxsarg)
A variant of save_item which takes multiple arguments
via an array sarg of SV* of length maxsarg.
SV* save_svref(SV **sptr)
Similar to save_scalar, but will reinstate a SV *.
void save_aptr(AV **aptr)
void save_hptr(HV **hptr)
Similar to save_svref, but localize AV * and HV *.
The Alias module implements localization of the basic
types within the caller's scope. People who are
interested in how to localize things in the containing
scope should take a look there too.
Subroutines
XSUBs and the Argument Stack
The XSUB mechanism is a simple way for Perl programs to
access C subroutines. An XSUB routine will have a stack
that contains the arguments from the Perl program, and a
way to map from the Perl data structures to a C
equivalent.
The stack arguments are accessible through the ST(n)
macro, which returns the n'th stack argument. Argument 0
is the first argument passed in the Perl subroutine call.
These arguments are SV*, and can be used anywhere an SV*
is used.
Most of the time, output from the C routine can be handled
through use of the RETVAL and OUTPUT directives. However,
there are some cases where the argument stack is not
already long enough to handle all the return values. An
example is the POSIX tzname() call, which takes no
arguments, but returns two, the local time zone's standard
and summer time abbreviations.
To handle this situation, the PPCODE directive is used and
the stack is extended using the macro:
EXTEND(SP, num);
where SP is the macro that represents the local copy of
the stack pointer, and num is the number of elements the
stack should be extended by.
Now that there is room on the stack, values can be pushed
on it using the macros to push IVs, doubles, strings, and
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SV pointers respectively:
PUSHi(IV)PUSHn(double)
PUSHp(char*, I32)
PUSHs(SV*)
And now the Perl program calling tzname, the two values
will be assigned as in:
($standard_abbrev, $summer_abbrev) = POSIX::tzname;
An alternate (and possibly simpler) method to pushing
values on the stack is to use the macros:
XPUSHi(IV)XPUSHn(double)
XPUSHp(char*, I32)
XPUSHs(SV*)
These macros automatically adjust the stack for you, if
needed. Thus, you do not need to call EXTEND to extend
the stack.
For more information, consult the perlxs manpage and the
perlxstut manpage.
Calling Perl Routines from within C Programs
There are four routines that can be used to call a Perl
subroutine from within a C program. These four are:
I32 perl_call_sv(SV*, I32);
I32 perl_call_pv(char*, I32);
I32 perl_call_method(char*, I32);
I32 perl_call_argv(char*, I32, register char**);
The routine most often used is perl_call_sv. The SV*
argument contains either the name of the Perl subroutine
to be called, or a reference to the subroutine. The
second argument consists of flags that control the context
in which the subroutine is called, whether or not the
subroutine is being passed arguments, how errors should be
trapped, and how to treat return values.
All four routines return the number of arguments that the
subroutine returned on the Perl stack.
When using any of these routines (except perl_call_argv),
the programmer must manipulate the Perl stack. These
include the following macros and functions:
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dSP
SP
PUSHMARK()
PUTBACK
SPAGAIN
ENTER
SAVETMPS
FREETMPS
LEAVE
XPUSH*()
POP*()
For a detailed description of calling conventions from C
to Perl, consult the perlcall manpage.
Memory Allocation
All memory meant to be used with the Perl API functions
should be manipulated using the macros described in this
section. The macros provide the necessary transparency
between differences in the actual malloc implementation
that is used within perl.
It is suggested that you enable the version of malloc that
is distributed with Perl. It keeps pools of various sizes
of unallocated memory in order to satisfy allocation
requests more quickly. However, on some platforms, it may
cause spurious malloc or free errors.
New(x, pointer, number, type);
Newc(x, pointer, number, type, cast);
Newz(x, pointer, number, type);
These three macros are used to initially allocate memory.
The first argument x was a "magic cookie" that was used to
keep track of who called the macro, to help when debugging
memory problems. However, the current code makes no use
of this feature (most Perl developers now use run-time
memory checkers), so this argument can be any number.
The second argument pointer should be the name of a
variable that will point to the newly allocated memory.
The third and fourth arguments number and type specify how
many of the specified type of data structure should be
allocated. The argument type is passed to sizeof. The
final argument to Newc, cast, should be used if the
pointer argument is different from the type argument.
Unlike the New and Newc macros, the Newz macro calls
memzero to zero out all the newly allocated memory.
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Renew(pointer, number, type);
Renewc(pointer, number, type, cast);
Safefree(pointer)
These three macros are used to change a memory buffer size
or to free a piece of memory no longer needed. The
arguments to Renew and Renewc match those of New and Newc
with the exception of not needing the "magic cookie"
argument.
Move(source, dest, number, type);
Copy(source, dest, number, type);
Zero(dest, number, type);
These three macros are used to move, copy, or zero out
previously allocated memory. The source and dest
arguments point to the source and destination starting
points. Perl will move, copy, or zero out number
instances of the size of the type data structure (using
the sizeof function).
PerlIO
The most recent development releases of Perl has been
experimenting with removing Perl's dependency on the
"normal" standard I/O suite and allowing other stdio
implementations to be used. This involves creating a new
abstraction layer that then calls whichever implementation
of stdio Perl was compiled with. All XSUBs should now use
the functions in the PerlIO abstraction layer and not make
any assumptions about what kind of stdio is being used.
For a complete description of the PerlIO abstraction,
consult the perlapio manpage.
Putting a C value on Perl stack
A lot of opcodes (this is an elementary operation in the
internal perl stack machine) put an SV* on the stack.
However, as an optimization the corresponding SV is
(usually) not recreated each time. The opcodes reuse
specially assigned SVs (targets) which are (as a
corollary) not constantly freed/created.
Each of the targets is created only once (but see the
section on Scratchpads and recursion below), and when an
opcode needs to put an integer, a double, or a string on
stack, it just sets the corresponding parts of its target
and puts the target on stack.
The macro to put this target on stack is PUSHTARG, and it
is directly used in some opcodes, as well as indirectly in
zillions of others, which use it via (X)PUSH[pni].
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Scratchpads
The question remains on when the SVs which are targets for
opcodes are created. The answer is that they are created
when the current unit -- a subroutine or a file (for
opcodes for statements outside of subroutines) -- is
compiled. During this time a special anonymous Perl array
is created, which is called a scratchpad for the current
unit.
A scratchpad keeps SVs which are lexicals for the current
unit and are targets for opcodes. One can deduce that an
SV lives on a scratchpad by looking on its flags: lexicals
have SVs_PADMY set, and targets have SVs_PADTMP set.
The correspondence between OPs and targets is not 1-to-1.
Different OPs in the compile tree of the unit can use the
same target, if this would not conflict with the expected
life of the temporary.
Scratchpads and recursion
In fact it is not 100% true that a compiled unit contains
a pointer to the scratchpad AV. In fact it contains a
pointer to an AV of (initially) one element, and this
element is the scratchpad AV. Why do we need an extra
level of indirection?
The answer is recursion, and maybe (sometime soon)
threads. Both these can create several execution pointers
going into the same subroutine. For the subroutine-child
not write over the temporaries for the subroutine-parent
(lifespan of which covers the call to the child), the
parent and the child should have different scratchpads.
(And the lexicals should be separate anyway!)
So each subroutine is born with an array of scratchpads
(of length 1). On each entry to the subroutine it is
checked that the current depth of the recursion is not
more than the length of this array, and if it is, new
scratchpad is created and pushed into the array.
The targets on this scratchpad are undefs, but they are
already marked with correct flags.
Compiled code
Code tree
Here we describe the internal form your code is converted
to by Perl. Start with a simple example:
$a = $b + $c;
This is converted to a tree similar to this one:
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assign-to
/ \
+ $a
/ \
$b $c
(but slightly more complicated). This tree reflects the
way Perl parsed your code, but has nothing to do with the
execution order. There is an additional "thread" going
through the nodes of the tree which shows the order of
execution of the nodes. In our simplified example above
it looks like:
$b ---> $c ---> + ---> $a ---> assign-to
But with the actual compile tree for $a = $b + $c it is
different: some nodes optimized away. As a corollary,
though the actual tree contains more nodes than our
simplified example, the execution order is the same as in
our example.
Examining the tree
If you have your perl compiled for debugging (usually done
with -D optimize=-g on Configure command line), you may
examine the compiled tree by specifying -Dx on the Perl
command line. The output takes several lines per node,
and for $b+$c it looks like this:
5 TYPE = add ===> 6
TARG = 1
FLAGS = (SCALAR,KIDS)
{
TYPE = null ===> (4)
(was rv2sv)
FLAGS = (SCALAR,KIDS)
{
3 TYPE = gvsv ===> 4
FLAGS = (SCALAR)
GV = main::b
}
}
{
TYPE = null ===> (5)
(was rv2sv)
FLAGS = (SCALAR,KIDS)
{
4 TYPE = gvsv ===> 5
FLAGS = (SCALAR)
GV = main::c
}
}
This tree has 5 nodes (one per TYPE specifier), only 3 of
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them are not optimized away (one per number in the left
column). The immediate children of the given node
correspond to {} pairs on the same level of indentation,
thus this listing corresponds to the tree:
add
/ \
null null
| |
gvsv gvsv
The execution order is indicated by ===> marks, thus it is
3 4 5 6 (node 6 is not included into above listing), i.e.,
gvsv gvsv add whatever.
Compile pass 1: check routines
The tree is created by the pseudo-compiler while yacc code
feeds it the constructions it recognizes. Since yacc works
bottom-up, so does the first pass of perl compilation.
What makes this pass interesting for perl developers is
that some optimization may be performed on this pass.
This is optimization by so-called check routines. The
correspondence between node names and corresponding check
routines is described in opcode.pl (do not forget to run
make regen_headers if you modify this file).
A check routine is called when the node is fully
constructed except for the execution-order thread. Since
at this time there are no back-links to the currently
constructed node, one can do most any operation to the
top-level node, including freeing it and/or creating new
nodes above/below it.
The check routine returns the node which should be
inserted into the tree (if the top-level node was not
modified, check routine returns its argument).
By convention, check routines have names ck_*. They are
usually called from new*OP subroutines (or convert) (which
in turn are called from perly.y).
Compile pass 1a: constant folding
Immediately after the check routine is called the returned
node is checked for being compile-time executable. If it
is (the value is judged to be constant) it is immediately
executed, and a constant node with the "return value" of
the corresponding subtree is substituted instead. The
subtree is deleted.
If constant folding was not performed, the execution-order
thread is created.
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Compile pass 2: context propagation
When a context for a part of compile tree is known, it is
propagated down through the tree. At this time the
context can have 5 values (instead of 2 for runtime
context): void, boolean, scalar, list, and lvalue. In
contrast with the pass 1 this pass is processed from top
to bottom: a node's context determines the context for its
children.
Additional context-dependent optimizations are performed
at this time. Since at this moment the compile tree
contains back-references (via "thread" pointers), nodes
cannot be free()d now. To allow optimized-away nodes at
this stage, such nodes are null()ified instead of
free()ing (i.e. their type is changed to OP_NULL).
Compile pass 3: peephole optimization
After the compile tree for a subroutine (or for an eval or
a file) is created, an additional pass over the code is
performed. This pass is neither top-down or bottom-up, but
in the execution order (with additional complications for
conditionals). These optimizations are done in the
subroutine peep(). Optimizations performed at this stage
are subject to the same restrictions as in the pass 2.
API LISTING
This is a listing of functions, macros, flags, and
variables that may be useful to extension writers or that
may be found while reading other extensions.
Note that all Perl API global variables must be referenced
with the PL_ prefix. Some macros are provided for
compatibility with the older, unadorned names, but this
support will be removed in a future release.
It is strongly recommended that all Perl API functions
that don't begin with perl be referenced with an explicit
Perl_ prefix.
The sort order of the listing is case insensitive, with
any occurrences of '_' ignored for the purpose of sorting.
av_clear
Clears an array, making it empty. Does not free
the memory used by the array itself.
void av_clear (AV* ar)
av_extend
Pre-extend an array. The key is the index to
which the array should be extended.
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void av_extend (AV* ar, I32 key)
av_fetch
Returns the SV at the specified index in the
array. The key is the index. If lval is set then
the fetch will be part of a store. Check that the
return value is non-null before dereferencing it
to a SV*.
See the section on Understanding the Magic of Tied
Hashes and Arrays for more information on how to
use this function on tied arrays.
SV** av_fetch (AV* ar, I32 key, I32 lval)
AvFILL Same as av_len(). Deprecated, use av_len()
instead.
av_len Returns the highest index in the array. Returns
-1 if the array is empty.
I32 av_len (AV* ar)
av_make Creates a new AV and populates it with a list of
SVs. The SVs are copied into the array, so they
may be freed after the call to av_make. The new
AV will have a reference count of 1.
AV* av_make (I32 size, SV** svp)
av_pop Pops an SV off the end of the array. Returns
&PL_sv_undef if the array is empty.
SV* av_pop (AV* ar)
av_push Pushes an SV onto the end of the array. The array
will grow automatically to accommodate the
addition.
void av_push (AV* ar, SV* val)
av_shift
Shifts an SV off the beginning of the array.
SV* av_shift (AV* ar)
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av_store
Stores an SV in an array. The array index is
specified as key. The return value will be NULL
if the operation failed or if the value did not
need to be actually stored within the array (as in
the case of tied arrays). Otherwise it can be
dereferenced to get the original SV*. Note that
the caller is responsible for suitably
incrementing the reference count of val before the
call, and decrementing it if the function returned
NULL.
See the section on Understanding the Magic of Tied
Hashes and Arrays for more information on how to
use this function on tied arrays.
SV** av_store (AV* ar, I32 key, SV* val)
av_undef
Undefines the array. Frees the memory used by the
array itself.
void av_undef (AV* ar)
av_unshift
Unshift the given number of undef values onto the
beginning of the array. The array will grow
automatically to accommodate the addition. You
must then use av_store to assign values to these
new elements.
void av_unshift (AV* ar, I32 num)
CLASS Variable which is setup by xsubpp to indicate the
class name for a C++ XS constructor. This is
always a char*. See THIS and the section on Using
XS With C++ in the perlxs manpage.
Copy The XSUB-writer's interface to the C memcpy
function. The s is the source, d is the
destination, n is the number of items, and t is
the type. May fail on overlapping copies. See
also Move.
void Copy( s, d, n, t )
croak This is the XSUB-writer's interface to Perl's die
function. Use this function the same way you use
the C printf function. See warn.
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CvSTASH Returns the stash of the CV.
HV* CvSTASH( SV* sv )
PL_DBsingle
When Perl is run in debugging mode, with the -d
switch, this SV is a boolean which indicates
whether subs are being single-stepped. Single-
stepping is automatically turned on after every
step. This is the C variable which corresponds to
Perl's $DB::single variable. See PL_DBsub.
PL_DBsub
When Perl is run in debugging mode, with the -d
switch, this GV contains the SV which holds the
name of the sub being debugged. This is the C
variable which corresponds to Perl's $DB::sub
variable. See PL_DBsingle. The sub name can be
found by
SvPV( GvSV( PL_DBsub ), len )
PL_DBtrace
Trace variable used when Perl is run in debugging
mode, with the -d switch. This is the C variable
which corresponds to Perl's $DB::trace variable.
See PL_DBsingle.
dMARK Declare a stack marker variable, mark, for the
XSUB. See MARK and dORIGMARK.
dORIGMARK
Saves the original stack mark for the XSUB. See
ORIGMARK.
PL_dowarn
The C variable which corresponds to Perl's $^W
warning variable.
dSP Declares a local copy of perl's stack pointer for
the XSUB, available via the SP macro. See SP.
dXSARGS Sets up stack and mark pointers for an XSUB,
calling dSP and dMARK. This is usually handled
automatically by xsubpp. Declares the items
variable to indicate the number of items on the
stack.
dXSI32 Sets up the ix variable for an XSUB which has
aliases. This is usually handled automatically by
xsubpp.
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do_binmode
Switches filehandle to binmode. iotype is what
IoTYPE(io) would contain.
do_binmode(fp, iotype, TRUE);
ENTER Opening bracket on a callback. See LEAVE and the
perlcall manpage.
ENTER;
EXTEND Used to extend the argument stack for an XSUB's
return values.
EXTEND( sp, int x )
fbm_compile
Analyses the string in order to make fast searches
on it using fbm_instr()-- the Boyer-Moore
algorithm.
void fbm_compile(SV* sv, U32 flags)
fbm_instr
Returns the location of the SV in the string
delimited by str and strend. It returns Nullch if
the string can't be found. The sv does not have
to be fbm_compiled, but the search will not be as
fast then.
char* fbm_instr(char *str, char *strend, SV *sv, U32 flags)
FREETMPS
Closing bracket for temporaries on a callback.
See SAVETMPS and the perlcall manpage.
FREETMPS;
G_ARRAY Used to indicate array context. See GIMME_V,
GIMME and the perlcall manpage.
G_DISCARD
Indicates that arguments returned from a callback
should be discarded. See the perlcall manpage.
G_EVAL Used to force a Perl eval wrapper around a
callback. See the perlcall manpage.
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GIMME A backward-compatible version of GIMME_V which can
only return G_SCALAR or G_ARRAY; in a void
context, it returns G_SCALAR.
GIMME_V The XSUB-writer's equivalent to Perl's wantarray.
Returns G_VOID, G_SCALAR or G_ARRAY for void,
scalar or array context, respectively.
G_NOARGS
Indicates that no arguments are being sent to a
callback. See the perlcall manpage.
G_SCALAR
Used to indicate scalar context. See GIMME_V,
GIMME, and the perlcall manpage.
gv_fetchmeth
Returns the glob with the given name and a defined
subroutine or NULL. The glob lives in the given
stash, or in the stashes accessible via @ISA and
@UNIVERSAL.
The argument level should be either 0 or -1. If
level==0, as a side-effect creates a glob with the
given name in the given stash which in the case of
success contains an alias for the subroutine, and
sets up caching info for this glob. Similarly for
all the searched stashes.
This function grants "SUPER" token as a postfix of
the stash name.
The GV returned from gv_fetchmeth may be a method
cache entry, which is not visible to Perl code.
So when calling perl_call_sv, you should not use
the GV directly; instead, you should use the
method's CV, which can be obtained from the GV
with the GvCV macro.
GV* gv_fetchmeth (HV* stash, char* name, STRLEN len, I32 level)
gv_fetchmethod
gv_fetchmethod_autoload
Returns the glob which contains the subroutine to
call to invoke the method on the stash. In fact
in the presence of autoloading this may be the
glob for "AUTOLOAD". In this case the
corresponding variable $AUTOLOAD is already setup.
The third parameter of gv_fetchmethod_autoload
determines whether AUTOLOAD lookup is performed if
the given method is not present: non-zero means
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yes, look for AUTOLOAD; zero means no, don't look
for AUTOLOAD. Calling gv_fetchmethod is
equivalent to calling gv_fetchmethod_autoload with
a non-zero autoload parameter.
These functions grant "SUPER" token as a prefix of
the method name.
Note that if you want to keep the returned glob
for a long time, you need to check for it being
"AUTOLOAD", since at the later time the call may
load a different subroutine due to $AUTOLOAD
changing its value. Use the glob created via a
side effect to do this.
These functions have the same side-effects and as
gv_fetchmeth with level==0. name should be
writable if contains ':' or '\''. The warning
against passing the GV returned by gv_fetchmeth to
perl_call_sv apply equally to these functions.
GV* gv_fetchmethod (HV* stash, char* name)
GV* gv_fetchmethod_autoload (HV* stash, char* name, I32 autoload)
G_VOID Used to indicate void context. See GIMME_V and
the perlcall manpage.
gv_stashpv
Returns a pointer to the stash for a specified
package. If create is set then the package will
be created if it does not already exist. If
create is not set and the package does not exist
then NULL is returned.
HV* gv_stashpv (char* name, I32 create)
gv_stashsv
Returns a pointer to the stash for a specified
package. See gv_stashpv.
HV* gv_stashsv (SV* sv, I32 create)
GvSV Return the SV from the GV.
HEf_SVKEY
This flag, used in the length slot of hash entries
and magic structures, specifies the structure
contains a SV* pointer where a char* pointer is to
be expected. (For information only--not to be
used).
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HeHASH Returns the computed hash stored in the hash
entry.
U32 HeHASH(HE* he)
HeKEY Returns the actual pointer stored in the key slot
of the hash entry. The pointer may be either
char* or SV*, depending on the value of HeKLEN().
Can be assigned to. The HePV() or HeSVKEY()
macros are usually preferable for finding the
value of a key.
char* HeKEY(HE* he)
HeKLEN If this is negative, and amounts to HEf_SVKEY, it
indicates the entry holds an SV* key. Otherwise,
holds the actual length of the key. Can be
assigned to. The HePV() macro is usually
preferable for finding key lengths.
int HeKLEN(HE* he)
HePV Returns the key slot of the hash entry as a char*
value, doing any necessary dereferencing of
possibly SV* keys. The length of the string is
placed in len (this is a macro, so do not use
&len). If you do not care about what the length
of the key is, you may use the global variable
PL_na, though this is rather less efficient than
using a local variable. Remember though, that
hash keys in perl are free to contain embedded
nulls, so using strlen() or similar is not a good
way to find the length of hash keys. This is very
similar to the SvPV() macro described elsewhere in
this document.
char* HePV(HE* he, STRLEN len)
HeSVKEY Returns the key as an SV*, or Nullsv if the hash
entry does not contain an SV* key.
HeSVKEY(HE* he)
HeSVKEY_force
Returns the key as an SV*. Will create and return
a temporary mortal SV* if the hash entry contains
only a char* key.
HeSVKEY_force(HE* he)
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HeSVKEY_set
Sets the key to a given SV*, taking care to set
the appropriate flags to indicate the presence of
an SV* key, and returns the same SV*.
HeSVKEY_set(HE* he, SV* sv)
HeVAL Returns the value slot (type SV*) stored in the
hash entry.
HeVAL(HE* he)
hv_clear
Clears a hash, making it empty.
void hv_clear (HV* tb)
hv_delete
Deletes a key/value pair in the hash. The value
SV is removed from the hash and returned to the
caller. The klen is the length of the key. The
flags value will normally be zero; if set to
G_DISCARD then NULL will be returned.
SV* hv_delete (HV* tb, char* key, U32 klen, I32 flags)
hv_delete_ent
Deletes a key/value pair in the hash. The value
SV is removed from the hash and returned to the
caller. The flags value will normally be zero; if
set to G_DISCARD then NULL will be returned. hash
can be a valid precomputed hash value, or 0 to ask
for it to be computed.
SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash)
hv_exists
Returns a boolean indicating whether the specified
hash key exists. The klen is the length of the
key.
bool hv_exists (HV* tb, char* key, U32 klen)
hv_exists_ent
Returns a boolean indicating whether the specified
hash key exists. hash can be a valid precomputed
hash value, or 0 to ask for it to be computed.
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bool hv_exists_ent (HV* tb, SV* key, U32 hash)
hv_fetch
Returns the SV which corresponds to the specified
key in the hash. The klen is the length of the
key. If lval is set then the fetch will be part
of a store. Check that the return value is non-
null before dereferencing it to a SV*.
See the section on Understanding the Magic of Tied
Hashes and Arrays for more information on how to
use this function on tied hashes.
SV** hv_fetch (HV* tb, char* key, U32 klen, I32 lval)
hv_fetch_ent
Returns the hash entry which corresponds to the
specified key in the hash. hash must be a valid
precomputed hash number for the given key, or 0 if
you want the function to compute it. IF lval is
set then the fetch will be part of a store. Make
sure the return value is non-null before accessing
it. The return value when tb is a tied hash is a
pointer to a static location, so be sure to make a
copy of the structure if you need to store it
somewhere.
See the section on Understanding the Magic of Tied
Hashes and Arrays for more information on how to
use this function on tied hashes.
HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash)
hv_iterinit
Prepares a starting point to traverse a hash
table.
I32 hv_iterinit (HV* tb)
Returns the number of keys in the hash (i.e. the
same as HvKEYS(tb)). The return value is
currently only meaningful for hashes without tie
magic.
NOTE: Before version 5.004_65, hv_iterinit used to
return the number of hash buckets that happen to
be in use. If you still need that esoteric value,
you can get it through the macro HvFILL(tb).
hv_iterkey
Returns the key from the current position of the
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hash iterator. See hv_iterinit.
char* hv_iterkey (HE* entry, I32* retlen)
hv_iterkeysv
Returns the key as an SV* from the current
position of the hash iterator. The return value
will always be a mortal copy of the key. Also see
hv_iterinit.
SV* hv_iterkeysv (HE* entry)
hv_iternext
Returns entries from a hash iterator. See
hv_iterinit.
HE* hv_iternext (HV* tb)
hv_iternextsv
Performs an hv_iternext, hv_iterkey, and
hv_iterval in one operation.
SV* hv_iternextsv (HV* hv, char** key, I32* retlen)
hv_iterval
Returns the value from the current position of the
hash iterator. See hv_iterkey.
SV* hv_iterval (HV* tb, HE* entry)
hv_magic
Adds magic to a hash. See sv_magic.
void hv_magic (HV* hv, GV* gv, int how)
HvNAME Returns the package name of a stash. See SvSTASH,
CvSTASH.
char* HvNAME (HV* stash)
hv_store
Stores an SV in a hash. The hash key is specified
as key and klen is the length of the key. The
hash parameter is the precomputed hash value; if
it is zero then Perl will compute it. The return
value will be NULL if the operation failed or if
the value did not need to be actually stored
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within the hash (as in the case of tied hashes).
Otherwise it can be dereferenced to get the
original SV*. Note that the caller is responsible
for suitably incrementing the reference count of
val before the call, and decrementing it if the
function returned NULL.
See the section on Understanding the Magic of Tied
Hashes and Arrays for more information on how to
use this function on tied hashes.
SV** hv_store (HV* tb, char* key, U32 klen, SV* val, U32 hash)
hv_store_ent
Stores val in a hash. The hash key is specified
as key. The hash parameter is the precomputed
hash value; if it is zero then Perl will compute
it. The return value is the new hash entry so
created. It will be NULL if the operation failed
or if the value did not need to be actually stored
within the hash (as in the case of tied hashes).
Otherwise the contents of the return value can be
accessed using the He??? macros described here.
Note that the caller is responsible for suitably
incrementing the reference count of val before the
call, and decrementing it if the function returned
NULL.
See the section on Understanding the Magic of Tied
Hashes and Arrays for more information on how to
use this function on tied hashes.
HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash)
hv_undef
Undefines the hash.
void hv_undef (HV* tb)
isALNUM Returns a boolean indicating whether the C char is
an ascii alphanumeric character or digit.
int isALNUM (char c)
isALPHA Returns a boolean indicating whether the C char is
an ascii alphabetic character.
int isALPHA (char c)
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isDIGIT Returns a boolean indicating whether the C char is
an ascii digit.
int isDIGIT (char c)
isLOWER Returns a boolean indicating whether the C char is
a lowercase character.
int isLOWER (char c)
isSPACE Returns a boolean indicating whether the C char is
whitespace.
int isSPACE (char c)
isUPPER Returns a boolean indicating whether the C char is
an uppercase character.
int isUPPER (char c)
items Variable which is setup by xsubpp to indicate the
number of items on the stack. See the section on
Variable-length Parameter Lists in the perlxs
manpage.
ix Variable which is setup by xsubpp to indicate
which of an XSUB's aliases was used to invoke it.
See the section on The ALIAS: Keyword in the
perlxs manpage.
LEAVE Closing bracket on a callback. See ENTER and the
perlcall manpage.
LEAVE;
looks_like_number
Test if an the content of an SV looks like a
number (or is a number).
int looks_like_number(SV*)
MARK Stack marker variable for the XSUB. See dMARK.
mg_clear
Clear something magical that the SV represents.
See sv_magic.
int mg_clear (SV* sv)
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mg_copy Copies the magic from one SV to another. See
sv_magic.
int mg_copy (SV *, SV *, char *, STRLEN)
mg_find Finds the magic pointer for type matching the SV.
See sv_magic.
MAGIC* mg_find (SV* sv, int type)
mg_free Free any magic storage used by the SV. See
sv_magic.
int mg_free (SV* sv)
mg_get Do magic after a value is retrieved from the SV.
See sv_magic.
int mg_get (SV* sv)
mg_len Report on the SV's length. See sv_magic.
U32 mg_len (SV* sv)
mg_magical
Turns on the magical status of an SV. See
sv_magic.
void mg_magical (SV* sv)
mg_set Do magic after a value is assigned to the SV. See
sv_magic.
int mg_set (SV* sv)
modglobal
modglobal is a general purpose, interpreter global
HV for use by extensions that need to keep
information on a per-interpreter basis. In a
pinch, it can also be used as a symbol table for
extensions to share data among each other. It is
a good idea to use keys prefixed by the package
name of the extension that owns the data.
Move The XSUB-writer's interface to the C memmove
function. The s is the source, d is the
destination, n is the number of items, and t is
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the type. Can do overlapping moves. See also
Copy.
void Move( s, d, n, t )
PL_na A convenience variable which is typically used
with SvPV when one doesn't care about the length
of the string. It is usually more efficient to
declare a local variable and use that instead.
New The XSUB-writer's interface to the C malloc
function.
void* New( x, void *ptr, int size, type )
newAV Creates a new AV. The reference count is set to
1.
AV* newAV (void)
Newc The XSUB-writer's interface to the C malloc
function, with cast.
void* Newc( x, void *ptr, int size, type, cast )
newCONSTSUB
Creates a constant sub equivalent to Perl sub FOO
() { 123 } which is eligible for inlining at
compile-time.
void newCONSTSUB(HV* stash, char* name, SV* sv)
newHV Creates a new HV. The reference count is set to
1.
HV* newHV (void)
newRV_inc
Creates an RV wrapper for an SV. The reference
count for the original SV is incremented.
SV* newRV_inc (SV* ref)
For historical reasons, "newRV" is a synonym for
"newRV_inc".
newRV_noinc
Creates an RV wrapper for an SV. The reference
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count for the original SV is not incremented.
SV* newRV_noinc (SV* ref)
NEWSV Creates a new SV. A non-zero len parameter
indicates the number of bytes of preallocated
string space the SV should have. An extra byte
for a tailing NUL is also reserved. (SvPOK is not
set for the SV even if string space is allocated.)
The reference count for the new SV is set to 1.
id is an integer id between 0 and 1299 (used to
identify leaks).
SV* NEWSV (int id, STRLEN len)
newSViv Creates a new SV and copies an integer into it.
The reference count for the SV is set to 1.
SV* newSViv (IV i)
newSVnv Creates a new SV and copies a double into it. The
reference count for the SV is set to 1.
SV* newSVnv (NV i)
newSVpv Creates a new SV and copies a string into it. The
reference count for the SV is set to 1. If len is
zero then Perl will compute the length.
SV* newSVpv (char* s, STRLEN len)
newSVpvf
Creates a new SV an initialize it with the string
formatted like sprintf.
SV* newSVpvf(const char* pat, ...);
newSVpvn
Creates a new SV and copies a string into it. The
reference count for the SV is set to 1. If len is
zero then Perl will create a zero length string.
SV* newSVpvn (char* s, STRLEN len)
newSVrv Creates a new SV for the RV, rv, to point to. If
rv is not an RV then it will be upgraded to one.
If classname is non-null then the new SV will be
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blessed in the specified package. The new SV is
returned and its reference count is 1.
SV* newSVrv (SV* rv, char* classname)
newSVsv Creates a new SV which is an exact duplicate of
the original SV.
SV* newSVsv (SV* old)
newXS Used by xsubpp to hook up XSUBs as Perl subs.
newXSproto
Used by xsubpp to hook up XSUBs as Perl subs.
Adds Perl prototypes to the subs.
Newz The XSUB-writer's interface to the C malloc
function. The allocated memory is zeroed with
memzero.
void* Newz( x, void *ptr, int size, type )
Nullav Null AV pointer.
Nullch Null character pointer.
Nullcv Null CV pointer.
Nullhv Null HV pointer.
Nullsv Null SV pointer.
ORIGMARK
The original stack mark for the XSUB. See
dORIGMARK.
perl_alloc
Allocates a new Perl interpreter. See the
perlembed manpage.
perl_call_argv
Performs a callback to the specified Perl sub.
See the perlcall manpage.
I32 perl_call_argv (char* subname, I32 flags, char** argv)
perl_call_method
Performs a callback to the specified Perl method.
The blessed object must be on the stack. See the
perlcall manpage.
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I32 perl_call_method (char* methname, I32 flags)
perl_call_pv
Performs a callback to the specified Perl sub.
See the perlcall manpage.
I32 perl_call_pv (char* subname, I32 flags)
perl_call_sv
Performs a callback to the Perl sub whose name is
in the SV. See the perlcall manpage.
I32 perl_call_sv (SV* sv, I32 flags)
perl_construct
Initializes a new Perl interpreter. See the
perlembed manpage.
perl_destruct
Shuts down a Perl interpreter. See the perlembed
manpage.
perl_eval_sv
Tells Perl to eval the string in the SV.
I32 perl_eval_sv (SV* sv, I32 flags)
perl_eval_pv
Tells Perl to eval the given string and return an
SV* result.
SV* perl_eval_pv (char* p, I32 croak_on_error)
perl_free
Releases a Perl interpreter. See the perlembed
manpage.
perl_get_av
Returns the AV of the specified Perl array. If
create is set and the Perl variable does not exist
then it will be created. If create is not set and
the variable does not exist then NULL is returned.
AV* perl_get_av (char* name, I32 create)
perl_get_cv
Returns the CV of the specified Perl sub. If
create is set and the Perl variable does not exist
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then it will be created. If create is not set and
the variable does not exist then NULL is returned.
CV* perl_get_cv (char* name, I32 create)
perl_get_hv
Returns the HV of the specified Perl hash. If
create is set and the Perl variable does not exist
then it will be created. If create is not set and
the variable does not exist then NULL is returned.
HV* perl_get_hv (char* name, I32 create)
perl_get_sv
Returns the SV of the specified Perl scalar. If
create is set and the Perl variable does not exist
then it will be created. If create is not set and
the variable does not exist then NULL is returned.
SV* perl_get_sv (char* name, I32 create)
perl_parse
Tells a Perl interpreter to parse a Perl script.
See the perlembed manpage.
perl_require_pv
Tells Perl to require a module.
void perl_require_pv (char* pv)
perl_run
Tells a Perl interpreter to run. See the
perlembed manpage.
POPi Pops an integer off the stack.
int POPi()
POPl Pops a long off the stack.
long POPl()
POPp Pops a string off the stack.
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POPn Pops a double off the stack.
double POPn()
POPs Pops an SV off the stack.
SV* POPs()
PUSHMARK
Opening bracket for arguments on a callback. See
PUTBACK and the perlcall manpage.
PUSHMARK(p)
PUSHi Push an integer onto the stack. The stack must
have room for this element. Handles 'set' magic.
See XPUSHi.
void PUSHi(int d)
PUSHn Push a double onto the stack. The stack must have
room for this element. Handles 'set' magic. See
XPUSHn.
void PUSHn(double d)
PUSHp Push a string onto the stack. The stack must have
room for this element. The len indicates the
length of the string. Handles 'set' magic. See
XPUSHp.
void PUSHp(char *c, int len )
PUSHs Push an SV onto the stack. The stack must have
room for this element. Does not handle 'set'
magic. See XPUSHs.
void PUSHs(sv)
PUSHu Push an unsigned integer onto the stack. The
stack must have room for this element. See
XPUSHu.
void PUSHu(unsigned int d)
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PUTBACK Closing bracket for XSUB arguments. This is
usually handled by xsubpp. See PUSHMARK and the
perlcall manpage for other uses.
PUTBACK;
Renew The XSUB-writer's interface to the C realloc
function.
void* Renew( void *ptr, int size, type )
Renewc The XSUB-writer's interface to the C realloc
function, with cast.
void* Renewc( void *ptr, int size, type, cast )
RETVAL Variable which is setup by xsubpp to hold the
return value for an XSUB. This is always the
proper type for the XSUB. See the section on The
RETVAL Variable in the perlxs manpage.
safefree
The XSUB-writer's interface to the C free
function.
safemalloc
The XSUB-writer's interface to the C malloc
function.
saferealloc
The XSUB-writer's interface to the C realloc
function.
savepv Copy a string to a safe spot. This does not use
an SV.
char* savepv (char* sv)
savepvn Copy a string to a safe spot. The len indicates
number of bytes to copy. This does not use an SV.
char* savepvn (char* sv, I32 len)
SAVETMPS
Opening bracket for temporaries on a callback.
See FREETMPS and the perlcall manpage.
SAVETMPS;
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SP Stack pointer. This is usually handled by xsubpp.
See dSP and SPAGAIN.
SPAGAIN Refetch the stack pointer. Used after a callback.
See the perlcall manpage.
SPAGAIN;
ST Used to access elements on the XSUB's stack.
SV* ST(int x)
strEQ Test two strings to see if they are equal.
Returns true or false.
int strEQ( char *s1, char *s2 )
strGE Test two strings to see if the first, s1, is
greater than or equal to the second, s2. Returns
true or false.
int strGE( char *s1, char *s2 )
strGT Test two strings to see if the first, s1, is
greater than the second, s2. Returns true or
false.
int strGT( char *s1, char *s2 )
strLE Test two strings to see if the first, s1, is less
than or equal to the second, s2. Returns true or
false.
int strLE( char *s1, char *s2 )
strLT Test two strings to see if the first, s1, is less
than the second, s2. Returns true or false.
int strLT( char *s1, char *s2 )
strNE Test two strings to see if they are different.
Returns true or false.
int strNE( char *s1, char *s2 )
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strnEQ Test two strings to see if they are equal. The
len parameter indicates the number of bytes to
compare. Returns true or false.
int strnEQ( char *s1, char *s2 )
strnNE Test two strings to see if they are different.
The len parameter indicates the number of bytes to
compare. Returns true or false.
int strnNE( char *s1, char *s2, int len )
sv_2mortal
Marks an SV as mortal. The SV will be destroyed
when the current context ends.
SV* sv_2mortal (SV* sv)
sv_bless
Blesses an SV into a specified package. The SV
must be an RV. The package must be designated by
its stash (see gv_stashpv()). The reference count
of the SV is unaffected.
SV* sv_bless (SV* sv, HV* stash)
sv_catpv
Concatenates the string onto the end of the string
which is in the SV. Handles 'get' magic, but not
'set' magic. See sv_catpv_mg.
void sv_catpv (SV* sv, char* ptr)
sv_catpv_mg
Like sv_catpv, but also handles 'set' magic.
void sv_catpv_mg (SV* sv, const char* ptr)
sv_catpvn
Concatenates the string onto the end of the string
which is in the SV. The len indicates number of
bytes to copy. Handles 'get' magic, but not 'set'
magic. See sv_catpvn_mg.
void sv_catpvn (SV* sv, char* ptr, STRLEN len)
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sv_catpvn_mg
Like sv_catpvn, but also handles 'set' magic.
void sv_catpvn_mg (SV* sv, char* ptr, STRLEN len)
sv_catpvf
Processes its arguments like sprintf and appends
the formatted output to an SV. Handles 'get'
magic, but not 'set' magic. SvSETMAGIC() must
typically be called after calling this function to
handle 'set' magic.
void sv_catpvf (SV* sv, const char* pat, ...)
sv_catpvf_mg
Like sv_catpvf, but also handles 'set' magic.
void sv_catpvf_mg (SV* sv, const char* pat, ...)
sv_catsv
Concatenates the string from SV ssv onto the end
of the string in SV dsv. Handles 'get' magic, but
not 'set' magic. See sv_catsv_mg.
void sv_catsv (SV* dsv, SV* ssv)
sv_catsv_mg
Like sv_catsv, but also handles 'set' magic.
void sv_catsv_mg (SV* dsv, SV* ssv)
sv_chop Efficient removal of characters from the beginning
of the string buffer. SvPOK(sv) must be true and
the ptr must be a pointer to somewhere inside the
string buffer. The ptr becomes the first
character of the adjusted string.
void sv_chop(SV* sv, char *ptr)
sv_cmp Compares the strings in two SVs. Returns -1, 0,
or 1 indicating whether the string in sv1 is less
than, equal to, or greater than the string in sv2.
I32 sv_cmp (SV* sv1, SV* sv2)
SvCUR Returns the length of the string which is in the
SV. See SvLEN.
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int SvCUR (SV* sv)
SvCUR_set
Set the length of the string which is in the SV.
See SvCUR.
void SvCUR_set (SV* sv, int val)
sv_dec Auto-decrement of the value in the SV.
void sv_dec (SV* sv)
sv_derived_from
Returns a boolean indicating whether the SV is
derived from the specified class. This is the
function that implements UNIVERSAL::isa. It works
for class names as well as for objects.
bool sv_derived_from _((SV* sv, char* name));
SvEND Returns a pointer to the last character in the
string which is in the SV. See SvCUR. Access the
character as
char* SvEND(sv)
sv_eq Returns a boolean indicating whether the strings
in the two SVs are identical.
I32 sv_eq (SV* sv1, SV* sv2)
SvGETMAGIC
Invokes mg_get on an SV if it has 'get' magic.
This macro evaluates its argument more than once.
void SvGETMAGIC(SV *sv)
SvGROW Expands the character buffer in the SV so that it
has room for the indicated number of bytes
(remember to reserve space for an extra trailing
NUL character). Calls sv_grow to perform the
expansion if necessary. Returns a pointer to the
character buffer.
char* SvGROW(SV* sv, STRLEN len)
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sv_grow Expands the character buffer in the SV. This will
use sv_unref and will upgrade the SV to SVt_PV.
Returns a pointer to the character buffer. Use
SvGROW.
sv_inc Auto-increment of the value in the SV.
void sv_inc (SV* sv)
sv_insert
Inserts a string at the specified offset/length
within the SV. Similar to the Perl substr()
function.
void sv_insert(SV *sv, STRLEN offset, STRLEN len,
char *str, STRLEN strlen)
SvIOK Returns a boolean indicating whether the SV
contains an integer.
int SvIOK (SV* SV)
SvIOK_off
Unsets the IV status of an SV.
void SvIOK_off (SV* sv)
SvIOK_on
Tells an SV that it is an integer.
void SvIOK_on (SV* sv)
SvIOK_only
Tells an SV that it is an integer and disables all
other OK bits.
void SvIOK_only (SV* sv)
SvIOKp Returns a boolean indicating whether the SV
contains an integer. Checks the private setting.
Use SvIOK.
int SvIOKp (SV* SV)
sv_isa Returns a boolean indicating whether the SV is
blessed into the specified class. This does not
check for subtypes; use sv_derived_from to verify
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an inheritance relationship.
int sv_isa (SV* sv, char* name)
sv_isobject
Returns a boolean indicating whether the SV is an
RV pointing to a blessed object. If the SV is not
an RV, or if the object is not blessed, then this
will return false.
int sv_isobject (SV* sv)
SvIV Coerces the given SV to an integer and returns it.
int SvIV (SV* sv)
SvIVX Returns the integer which is stored in the SV,
assuming SvIOK is true.
int SvIVX (SV* sv)
SvLEN Returns the size of the string buffer in the SV.
See SvCUR.
int SvLEN (SV* sv)
sv_len Returns the length of the string in the SV. Use
SvCUR.
STRLEN sv_len (SV* sv)
sv_magic
Adds magic to an SV.
void sv_magic (SV* sv, SV* obj, int how, char* name, I32 namlen)
sv_mortalcopy
Creates a new SV which is a copy of the original
SV. The new SV is marked as mortal.
SV* sv_mortalcopy (SV* oldsv)
sv_newmortal
Creates a new SV which is mortal. The reference
count of the SV is set to 1.
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SV* sv_newmortal (void)
SvNIOK Returns a boolean indicating whether the SV
contains a number, integer or double.
int SvNIOK (SV* SV)
SvNIOK_off
Unsets the NV/IV status of an SV.
void SvNIOK_off (SV* sv)
SvNIOKp Returns a boolean indicating whether the SV
contains a number, integer or double. Checks the
private setting. Use SvNIOK.
int SvNIOKp (SV* SV)
PL_sv_no
This is the false SV. See PL_sv_yes. Always
refer to this as &PL_sv_no.
SvNOK Returns a boolean indicating whether the SV
contains a double.
int SvNOK (SV* SV)
SvNOK_off
Unsets the NV status of an SV.
void SvNOK_off (SV* sv)
SvNOK_on
Tells an SV that it is a double.
void SvNOK_on (SV* sv)
SvNOK_only
Tells an SV that it is a double and disables all
other OK bits.
void SvNOK_only (SV* sv)
SvNOKp Returns a boolean indicating whether the SV
contains a double. Checks the private setting.
Use SvNOK.
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int SvNOKp (SV* SV)
SvNV Coerce the given SV to a double and return it.
double SvNV (SV* sv)
SvNVX Returns the double which is stored in the SV,
assuming SvNOK is true.
double SvNVX (SV* sv)
SvOK Returns a boolean indicating whether the value is
an SV.
int SvOK (SV* sv)
SvOOK Returns a boolean indicating whether the SvIVX is
a valid offset value for the SvPVX. This hack is
used internally to speed up removal of characters
from the beginning of a SvPV. When SvOOK is true,
then the start of the allocated string buffer is
really (SvPVX - SvIVX).
int SvOOK(SV* sv)
SvPOK Returns a boolean indicating whether the SV
contains a character string.
int SvPOK (SV* SV)
SvPOK_off
Unsets the PV status of an SV.
void SvPOK_off (SV* sv)
SvPOK_on
Tells an SV that it is a string.
void SvPOK_on (SV* sv)
SvPOK_only
Tells an SV that it is a string and disables all
other OK bits.
void SvPOK_only (SV* sv)
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SvPOKp Returns a boolean indicating whether the SV
contains a character string. Checks the private
setting. Use SvPOK.
int SvPOKp (SV* SV)
SvPV Returns a pointer to the string in the SV, or a
stringified form of the SV if the SV does not
contain a string. Handles 'get' magic.
char* SvPV (SV* sv, STRLEN len)
SvPV_force
Like <SvPV> but will force the SV into becoming a
string (SvPOK). You want force if you are going
to update the SvPVX directly.
char* SvPV_force(SV* sv, STRLEN len)
SvPVX Returns a pointer to the string in the SV. The SV
must contain a string.
char* SvPVX (SV* sv)
SvREFCNT
Returns the value of the object's reference count.
int SvREFCNT (SV* sv)
SvREFCNT_dec
Decrements the reference count of the given SV.
void SvREFCNT_dec (SV* sv)
SvREFCNT_inc
Increments the reference count of the given SV.
void SvREFCNT_inc (SV* sv)
SvROK Tests if the SV is an RV.
int SvROK (SV* sv)
SvROK_off
Unsets the RV status of an SV.
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void SvROK_off (SV* sv)
SvROK_on
Tells an SV that it is an RV.
void SvROK_on (SV* sv)
SvRV Dereferences an RV to return the SV.
SV* SvRV (SV* sv)
SvSETMAGIC
Invokes mg_set on an SV if it has 'set' magic.
This macro evaluates its argument more than once.
void SvSETMAGIC( SV *sv )
sv_setiv
Copies an integer into the given SV. Does not
handle 'set' magic. See sv_setiv_mg.
void sv_setiv (SV* sv, IV num)
sv_setiv_mg
Like sv_setiv, but also handles 'set' magic.
void sv_setiv_mg (SV* sv, IV num)
sv_setnv
Copies a double into the given SV. Does not
handle 'set' magic. See sv_setnv_mg.
void sv_setnv (SV* sv, double num)
sv_setnv_mg
Like sv_setnv, but also handles 'set' magic.
void sv_setnv_mg (SV* sv, double num)
sv_setpv
Copies a string into an SV. The string must be
null-terminated. Does not handle 'set' magic.
See sv_setpv_mg.
void sv_setpv (SV* sv, const char* ptr)
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sv_setpv_mg
Like sv_setpv, but also handles 'set' magic.
void sv_setpv_mg (SV* sv, const char* ptr)
sv_setpviv
Copies an integer into the given SV, also updating
its string value. Does not handle 'set' magic.
See sv_setpviv_mg.
void sv_setpviv (SV* sv, IV num)
sv_setpviv_mg
Like sv_setpviv, but also handles 'set' magic.
void sv_setpviv_mg (SV* sv, IV num)
sv_setpvn
Copies a string into an SV. The len parameter
indicates the number of bytes to be copied. Does
not handle 'set' magic. See sv_setpvn_mg.
void sv_setpvn (SV* sv, const char* ptr, STRLEN len)
sv_setpvn_mg
Like sv_setpvn, but also handles 'set' magic.
void sv_setpvn_mg (SV* sv, const char* ptr, STRLEN len)
sv_setpvf
Processes its arguments like sprintf and sets an
SV to the formatted output. Does not handle 'set'
magic. See sv_setpvf_mg.
void sv_setpvf (SV* sv, const char* pat, ...)
sv_setpvf_mg
Like sv_setpvf, but also handles 'set' magic.
void sv_setpvf_mg (SV* sv, const char* pat, ...)
sv_setref_iv
Copies an integer into a new SV, optionally
blessing the SV. The rv argument will be upgraded
to an RV. That RV will be modified to point to
the new SV. The classname argument indicates the
package for the blessing. Set classname to Nullch
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to avoid the blessing. The new SV will be
returned and will have a reference count of 1.
SV* sv_setref_iv (SV *rv, char *classname, IV iv)
sv_setref_nv
Copies a double into a new SV, optionally blessing
the SV. The rv argument will be upgraded to an
RV. That RV will be modified to point to the new
SV. The classname argument indicates the package
for the blessing. Set classname to Nullch to
avoid the blessing. The new SV will be returned
and will have a reference count of 1.
SV* sv_setref_nv (SV *rv, char *classname, double nv)
sv_setref_pv
Copies a pointer into a new SV, optionally
blessing the SV. The rv argument will be upgraded
to an RV. That RV will be modified to point to
the new SV. If the pv argument is NULL then
PL_sv_undef will be placed into the SV. The
classname argument indicates the package for the
blessing. Set classname to Nullch to avoid the
blessing. The new SV will be returned and will
have a reference count of 1.
SV* sv_setref_pv (SV *rv, char *classname, void* pv)
Do not use with integral Perl types such as HV,
AV, SV, CV, because those objects will become
corrupted by the pointer copy process.
Note that sv_setref_pvn copies the string while
this copies the pointer.
sv_setref_pvn
Copies a string into a new SV, optionally blessing
the SV. The length of the string must be
specified with n. The rv argument will be
upgraded to an RV. That RV will be modified to
point to the new SV. The classname argument
indicates the package for the blessing. Set
classname to Nullch to avoid the blessing. The
new SV will be returned and will have a reference
count of 1.
SV* sv_setref_pvn (SV *rv, char *classname, char* pv, I32 n)
Note that sv_setref_pv copies the pointer while
this copies the string.
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SvSetSV Calls sv_setsv if dsv is not the same as ssv. May
evaluate arguments more than once.
void SvSetSV (SV* dsv, SV* ssv)
SvSetSV_nosteal
Calls a non-destructive version of sv_setsv if dsv
is not the same as ssv. May evaluate arguments
more than once.
void SvSetSV_nosteal (SV* dsv, SV* ssv)
sv_setsv
Copies the contents of the source SV ssv into the
destination SV dsv. The source SV may be
destroyed if it is mortal. Does not handle 'set'
magic. See the macro forms SvSetSV,
SvSetSV_nosteal and sv_setsv_mg.
void sv_setsv (SV* dsv, SV* ssv)
sv_setsv_mg
Like sv_setsv, but also handles 'set' magic.
void sv_setsv_mg (SV* dsv, SV* ssv)
sv_setuv
Copies an unsigned integer into the given SV.
Does not handle 'set' magic. See sv_setuv_mg.
void sv_setuv (SV* sv, UV num)
sv_setuv_mg
Like sv_setuv, but also handles 'set' magic.
void sv_setuv_mg (SV* sv, UV num)
SvSTASH Returns the stash of the SV.
HV* SvSTASH (SV* sv)
SvTAINT Taints an SV if tainting is enabled
void SvTAINT (SV* sv)
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SvTAINTED
Checks to see if an SV is tainted. Returns TRUE if
it is, FALSE if not.
int SvTAINTED (SV* sv)
SvTAINTED_off
Untaints an SV. Be very careful with this routine,
as it short-circuits some of Perl's fundamental
security features. XS module authors should not
use this function unless they fully understand all
the implications of unconditionally untainting the
value. Untainting should be done in the standard
perl fashion, via a carefully crafted regexp,
rather than directly untainting variables.
void SvTAINTED_off (SV* sv)
SvTAINTED_on
Marks an SV as tainted.
void SvTAINTED_on (SV* sv)
SVt_IV Integer type flag for scalars. See svtype.
SVt_PV Pointer type flag for scalars. See svtype.
SVt_PVAV
Type flag for arrays. See svtype.
SVt_PVCV
Type flag for code refs. See svtype.
SVt_PVHV
Type flag for hashes. See svtype.
SVt_PVMG
Type flag for blessed scalars. See svtype.
SVt_NV Double type flag for scalars. See svtype.
SvTRUE Returns a boolean indicating whether Perl would
evaluate the SV as true or false, defined or
undefined. Does not handle 'get' magic.
int SvTRUE (SV* sv)
SvTYPE Returns the type of the SV. See svtype.
svtype SvTYPE (SV* sv)
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svtype An enum of flags for Perl types. These are found
in the file sv.h in the svtype enum. Test these
flags with the SvTYPE macro.
PL_sv_undef
This is the undef SV. Always refer to this as
&PL_sv_undef.
sv_unref
Unsets the RV status of the SV, and decrements the
reference count of whatever was being referenced
by the RV. This can almost be thought of as a
reversal of newSVrv. See SvROK_off.
void sv_unref (SV* sv)
SvUPGRADE
Used to upgrade an SV to a more complex form.
Uses sv_upgrade to perform the upgrade if
necessary. See svtype.
bool SvUPGRADE (SV* sv, svtype mt)
sv_upgrade
Upgrade an SV to a more complex form. Use
SvUPGRADE. See svtype.
sv_usepvn
Tells an SV to use ptr to find its string value.
Normally the string is stored inside the SV but
sv_usepvn allows the SV to use an outside string.
The ptr should point to memory that was allocated
by malloc. The string length, len, must be
supplied. This function will realloc the memory
pointed to by ptr, so that pointer should not be
freed or used by the programmer after giving it to
sv_usepvn. Does not handle 'set' magic. See
sv_usepvn_mg.
void sv_usepvn (SV* sv, char* ptr, STRLEN len)
sv_usepvn_mg
Like sv_usepvn, but also handles 'set' magic.
void sv_usepvn_mg (SV* sv, char* ptr, STRLEN len)
sv_vcatpvfn(sv, pat, patlen, args, svargs, svmax,
used_locale)
Processes its arguments like vsprintf and appends
the formatted output to an SV. Uses an array of
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SVs if the C style variable argument list is
missing (NULL). Indicates if locale information
has been used for formatting.
void sv_catpvfn _((SV* sv, const char* pat, STRLEN patlen,
va_list *args, SV **svargs, I32 svmax,
bool *used_locale));
sv_vsetpvfn(sv, pat, patlen, args, svargs, svmax,
used_locale)
Works like vcatpvfn but copies the text into the
SV instead of appending it.
void sv_setpvfn _((SV* sv, const char* pat, STRLEN patlen,
va_list *args, SV **svargs, I32 svmax,
bool *used_locale));
SvUV Coerces the given SV to an unsigned integer and
returns it.
UV SvUV(SV* sv)
SvUVX Returns the unsigned integer which is stored in
the SV, assuming SvIOK is true.
UV SvUVX(SV* sv)
PL_sv_yes
This is the true SV. See PL_sv_no. Always refer
to this as &PL_sv_yes.
THIS Variable which is setup by xsubpp to designate the
object in a C++ XSUB. This is always the proper
type for the C++ object. See CLASS and the
section on Using XS With C++ in the perlxs
manpage.
toLOWER Converts the specified character to lowercase.
int toLOWER (char c)
toUPPER Converts the specified character to uppercase.
int toUPPER (char c)
warn This is the XSUB-writer's interface to Perl's warn
function. Use this function the same way you use
the C printf function. See croak().
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XPUSHi Push an integer onto the stack, extending the
stack if necessary. Handles 'set' magic. See
PUSHi.
XPUSHi(int d)
XPUSHn Push a double onto the stack, extending the stack
if necessary. Handles 'set' magic. See PUSHn.
XPUSHn(double d)
XPUSHp Push a string onto the stack, extending the stack
if necessary. The len indicates the length of the
string. Handles 'set' magic. See PUSHp.
XPUSHp(char *c, int len)
XPUSHs Push an SV onto the stack, extending the stack if
necessary. Does not handle 'set' magic. See
PUSHs.
XPUSHs(sv)
XPUSHu Push an unsigned integer onto the stack, extending
the stack if necessary. See PUSHu.
XS Macro to declare an XSUB and its C parameter list.
This is handled by xsubpp.
XSRETURN
Return from XSUB, indicating number of items on
the stack. This is usually handled by xsubpp.
XSRETURN(int x)
XSRETURN_EMPTY
Return an empty list from an XSUB immediately.
XSRETURN_EMPTY;
XSRETURN_IV
Return an integer from an XSUB immediately. Uses
XST_mIV.
XSRETURN_IV(IV v)
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XSRETURN_NO
Return &PL_sv_no from an XSUB immediately. Uses
XST_mNO.
XSRETURN_NO;
XSRETURN_NV
Return an double from an XSUB immediately. Uses
XST_mNV.
XSRETURN_NV(NV v)
XSRETURN_PV
Return a copy of a string from an XSUB
immediately. Uses XST_mPV.
XSRETURN_PV(char *v)
XSRETURN_UNDEF
Return &PL_sv_undef from an XSUB immediately.
Uses XST_mUNDEF.
XSRETURN_UNDEF;
XSRETURN_YES
Return &PL_sv_yes from an XSUB immediately. Uses
XST_mYES.
XSRETURN_YES;
XST_mIV Place an integer into the specified position i on
the stack. The value is stored in a new mortal
SV.
XST_mIV( int i, IV v )
XST_mNV Place a double into the specified position i on
the stack. The value is stored in a new mortal
SV.
XST_mNV( int i, NV v )
XST_mNO Place &PL_sv_no into the specified position i on
the stack.
XST_mNO( int i )
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XST_mPV Place a copy of a string into the specified
position i on the stack. The value is stored in a
new mortal SV.
XST_mPV( int i, char *v )
XST_mUNDEF
Place &PL_sv_undef into the specified position i
on the stack.
XST_mUNDEF( int i )
XST_mYES
Place &PL_sv_yes into the specified position i on
the stack.
XST_mYES( int i )
XS_VERSION
The version identifier for an XS module. This is
usually handled automatically by
ExtUtils::MakeMaker. See XS_VERSION_BOOTCHECK.
XS_VERSION_BOOTCHECK
Macro to verify that a PM module's $VERSION
variable matches the XS module's XS_VERSION
variable. This is usually handled automatically
by xsubpp. See the section on The VERSIONCHECK:
Keyword in the perlxs manpage.
Zero The XSUB-writer's interface to the C memzero
function. The d is the destination, n is the
number of items, and t is the type.
void Zero( d, n, t )
AUTHORS
Until May 1997, this document was maintained by Jeff
Okamoto <okamoto@corp.hp.com>. It is now maintained as
part of Perl itself.
With lots of help and suggestions from Dean Roehrich,
Malcolm Beattie, Andreas Koenig, Paul Hudson, Ilya
Zakharevich, Paul Marquess, Neil Bowers, Matthew Green,
Tim Bunce, Spider Boardman, Ulrich Pfeifer, Stephen
McCamant, and Gurusamy Sarathy.
API Listing originally by Dean Roehrich
<roehrich@cray.com>.
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