ExtUtils::CChecker(3) User Contributed Perl DocumentationExtUtils::CChecker(3)NAME
"ExtUtils::CChecker" - configure-time utilities for using C headers,
libraries, or OS features
SYNOPSIS
use Module::Build;
use ExtUtils::CChecker;
my $cc = ExtUtils::CChecker->new;
$cc->assert_compile_run(
diag => "no PF_MOONLASER",
source => <<'EOF' );
#include <stdio.h>
#include <sys/socket.h>
int main(int argc, char *argv[]) {
printf("PF_MOONLASER is %d\n", PF_MOONLASER);
return 0;
}
EOF
Module::Build->new(
...
)->create_build_script;
DESCRIPTION
Often Perl modules are written to wrap functionality found in existing
C headers, libraries, or to use OS-specific features. It is useful in
the Build.PL or Makefile.PL file to check for the existance of these
requirements before attempting to actually build the module.
Objects in this class provide an extension around ExtUtils::CBuilder to
simplify the creation of a .c file, compiling, linking and running it,
to test if a certain feature is present.
It may also be necessary to search for the correct library to link
against, or for the right include directories to find header files in.
This class also provides assistance here.
CONSTRUCTOR
$cc = ExtUtils::CChecker->new( %args )
Returns a new instance of a "ExtUtils::CChecker" object. Takes the
following named parameters:
defines_to => PATH
If given, defined symbols will be written to a C preprocessor
.h file of the given name, instead of by adding extra
"-DSYMBOL" arguments to the compiler flags.
quiet => BOOL
If given, sets the "quiet" option to the underlying
"ExtUtils::CBuilder" instance. If absent, defaults to enabled.
To disable quietness, i.e. to print more verbosely, pass a
defined-but-false value, such as 0.
METHODS
$dirs = $cc->include_dirs
Returns the currently-configured include directories in an ARRAY
reference.
$flags = $cc->extra_compiler_flags
Returns the currently-configured extra compiler flags in an ARRAY
reference.
$flags = $cc->extra_linker_flags
Returns the currently-configured extra linker flags in an ARRAY
reference.
$cc->push_include_dirs( @dirs )
Adds more include directories
$cc->push_extra_compiler_flags( @flags )
Adds more compiler flags
$cc->push_extra_linker_flags( @flags )
Adds more linker flags
$success = $cc->try_compile_run( %args )
$success = $cc->try_compile_run( $source )
Try to compile, link, and execute a C program whose source is given.
Returns true if the program compiled and linked, and exited
successfully. Returns false if any of these steps fail.
Takes the following named arguments. If a single argument is given,
that is taken as the source string.
· source => STRING
The source code of the C program to try compiling, building,
and running.
· extra_compiler_flags => ARRAY
Optional. If specified, pass extra flags to the compiler.
· extra_linker_flags => ARRAY
Optional. If specified, pass extra flags to the linker.
· define => STRING
Optional. If specified, then the named symbol will be defined
if the program ran successfully. This will either on the C
compiler commandline (by passing an option "-DSYMBOL"), or in
the "defines_to" file.
$cc->assert_compile_run( %args )
Calls "try_compile_run". If it fails, die with an "OS unsupported"
message. Useful to call from Build.PL or Makefile.PL.
Takes one extra optional argument:
· diag => STRING
If present, this string will be appended to the failure message
if one is generated. It may provide more useful information to
the user on why the OS is unsupported.
$success = $cc->try_find_include_dirs_for( %args )
Try to compile, link and execute the given source, using extra include
directories.
When a usable combination is found, the directories required are stored
in the object for use in further compile operations, or returned by
"include_dirs". The method then returns true.
If no a usable combination is found, it returns false.
Takes the following arguments:
· source => STRING
Source code to compile
· dirs => ARRAY of ARRAYs
Gives a list of sets of dirs. Each set of dirs should be
strings in its own array reference.
· define => STRING
Optional. If specified, then the named symbol will be defined
if the program ran successfully. This will either on the C
compiler commandline (by passing an option "-DSYMBOL"), or in
the "defines_to" file.
$success = $cc->try_find_libs_for( %args )
Try to compile, link and execute the given source, when linked against
a given set of extra libraries.
When a usable combination is found, the libraries required are stored
in the object for use in further link operations, or returned by
"extra_linker_flags". The method then returns true.
If no usable combination is found, it returns false.
Takes the following arguments:
· source => STRING
Source code to compile
· libs => ARRAY of STRINGs
Gives a list of sets of libraries. Each set of libraries should
be space-separated.
· define => STRING
Optional. If specified, then the named symbol will be defined
if the program ran successfully. This will either on the C
compiler commandline (by passing an option "-DSYMBOL"), or in
the "defines_to" file.
$cc->find_include_dirs_for( %args )
$cc->find_libs_for( %args )
Calls "try_find_include_dirs_for" or "try_find_libs_for" respectively.
If it fails, die with an "OS unsupported" message.
Each method takes one extra optional argument:
· diag => STRING
If present, this string will be appended to the failure message
if one is generated. It may provide more useful information to
the user on why the OS is unsupported.
$mb = $cc->new_module_build( %args )
Construct and return a new Module::Build object, preconfigured with the
"include_dirs", "extra_compiler_flags" and "extra_linker_flags" options
that have been configured on this object, by the above methods.
This is provided as a simple shortcut for the common use case, that a
Build.PL file is using the "ExtUtils::CChecker" object to detect the
required arguments to pass.
EXAMPLES
Socket Libraries
Some operating systems provide the BSD sockets API in their primary
libc. Others keep it in a separate library which should be linked
against. The following example demonstrates how this would be handled.
use ExtUtils::CChecker;
my $cc = ExtUtils::CChecker->new;
$cc->find_libs_for(
diag => "no socket()",
libs => [ "", "socket nsl" ],
source => q[
#include <sys/socket.h>
int main(int argc, char *argv) {
int fd = socket(PF_INET, SOCK_STREAM, 0);
if(fd < 0)
return 1;
return 0;
}
] );
$cc->new_module_build(
module_name => "Your::Name::Here",
requires => {
'IO::Socket' => 0,
},
...
)->create_build_script;
By using the "new_module_build" method, the detected
"extra_linker_flags" value has been automatically passed into the new
"Module::Build" object.
Testing For Optional Features
Sometimes a function or ability may be optionally provided by the OS,
or you may wish your module to be useable when only partial support is
provided, without requiring it all to be present. In these cases it is
traditional to detect the presence of this optional feature in the
Build.PL script, and define a symbol to declare this fact if it is
found. The XS code can then use this symbol to select between differing
implementations. For example, the Build.PL:
use ExtUtils::CChecker;
my $cc = ExtUtils::CChecker->new;
$cc->try_compile_run(
define => "HAVE_MANGO",
source => <<'EOF' );
#include <mango.h>
#include <unistd.h>
int main(void) {
if(mango() != 0)
exit(1);
exit(0);
}
EOF
$cc->new_module_build(
...
)->create_build_script;
If the C code compiles and runs successfully, and exits with a true
status, the symbol "HAVE_MANGO" will be defined on the compiler
commandline. This allows the XS code to detect it, for example
int
mango()
CODE:
#ifdef HAVE_MANGO
RETVAL = mango();
#else
croak("mango() not implemented");
#endif
OUTPUT:
RETVAL
This module will then still compile even if the operating system lacks
this particular function. Trying to invoke the function at runtime will
simply throw an exception.
Linux Kernel Headers
Operating systems built on top of the Linux kernel often share a looser
association with their kernel version than most other operating
systems. It may be the case that the running kernel is newer,
containing more features, than the distribution's libc headers would
believe. In such circumstances it can be difficult to make use of new
socket options, "ioctl()"s, etc.. without having the constants that
define them and their parameter structures, because the relevant header
files are not visible to the compiler. In this case, there may be
little choice but to pull in some of the kernel header files, which
will provide the required constants and structures.
The Linux kernel headers can be found using the /lib/modules directory.
A fragment in Build.PL like the following, may be appropriate.
chomp( my $uname_r = `uname -r` );
my @dirs = (
[],
[ "/lib/modules/$uname_r/source/include" ],
);
$cc->find_include_dirs_for(
diag => "no PF_MOONLASER",
dirs => \@dirs,
source => <<'EOF' );
#include <sys/socket.h>
#include <moon/laser.h>
int family = PF_MOONLASER;
struct laserwl lwl;
int main(int argc, char *argv[]) {
return 0;
}
EOF
This fragment will first try to compile the program as it stands,
hoping that the libc headers will be sufficient. If it fails, it will
then try including the kernel headers, which should make the constant
and structure visible, allowing the program to compile.
Creating an "#include" file
Sometimes, rather than setting defined symbols on the compiler
commandline, it is preferrable to have them written to a C preprocessor
include (.h) file. This may be beneficial for cross-platform
portability concerns, as not all C compilers may take extra "-D"
arguments on the command line, or platforms may have small length
restrictions on the length of a command line.
use ExtUtils::CChecker;
my $cc = ExtUtils::CChecker->new(
defines_to => "mymodule-config.h",
);
$cc->try_compile_run(
define => "HAVE_MANGO",
source => <<'EOF' );
#include <mango.h>
#include <unistd.h>
#include "mymodule-config.h"
int main(void) {
if(mango() != 0)
exit(1);
exit(0);
}
EOF
Because the mymodule-config.h file is written and flushed after every
define operation, it will still be useable in later C fragments to test
for features detected in earlier ones.
It is suggested not to name the file simply config.h, as the core of
Perl itself has a file of that name containing its own compile-time
detected configuration. A confusion between the two could lead to
surprising results.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
perl v5.18.2 2013-12-12 ExtUtils::CChecker(3)
