Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)_________________________________________________________________NAME
Tcl_OpenFileChannel, Tcl_OpenCommandChannel, Tcl_Close,
Tcl_Read, Tcl_Gets, Tcl_Write, Tcl_Flush, Tcl_Seek,
Tcl_Tell, Tcl_Eof, Tcl_InputBlocked, Tcl_GetChannelOption,
Tcl_SetChannelOption - buffered I/O facilities using chan-
nels
SYNOPSIS
#include <tcl.h>
typedef ... Tcl_Channel;
Tcl_Channel
Tcl_OpenFileChannel(interp, fileName, mode, permissions)
Tcl_Channel
Tcl_OpenCommandChannel(interp, argc, argv, flags)
Tcl_Channel
Tcl_MakeFileChannel(inOsFile, outOsFile, readOrWrite)
Tcl_Channel
Tcl_GetChannel(interp, channelName, modePtr)
void
Tcl_RegisterChannel(interp, channel)
int
Tcl_UnregisterChannel(interp, channel)
int
Tcl_Close(interp, channel)
int
Tcl_Read(channel, buf, toRead)
int
Tcl_Gets(channel, lineRead)
int
Tcl_Write(channel, buf, toWrite)
int
Tcl_Flush(channel)
int
Tcl_Seek(channel, offset, seekMode)
int
Tcl_Tell(channel)
int
Tcl 7.5 1
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
Tcl_GetChannelOption(channel, optionName, optionValue)
int
Tcl_SetChannelOption(interp, channel, optionName, newValue)
int
Tcl_Eof(channel)
int
Tcl_InputBlocked(channel)
int
Tcl_InputBuffered(channel)ARGUMENTS
Tcl_Interp *interp (in) Used for
error
reporting
and to look
up a chan-
nel regis-
tered in
it.
char *fileName (in) The name of
a local or
network
file.
char *mode (in) Specifies
how the
file is to
be
accessed.
May have
any of the
values
allowed for
the mode
argument to
the Tcl
open com-
mand. For
Tcl_Open-
Command-
Channel,
may be
NULL.
int permissions (in) POSIX-style
permission
flags such
as 0644.
Tcl 7.5 2
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
If a new
file is
created,
these per-
missions
will be set
on the cre-
ated file.
int argc (in) The number
of elements
in argv.
char **argv (in) Arguments
for con-
structing a
command
pipeline.
These val-
ues have
the same
meaning as
the non-
switch
arguments
to the Tcl
exec com-
mand.
int flags (in) Specifies
the dispo-
sition of
the stdio
handles in
pipeline:
OR-ed com-
bination of
TCL_STDIN,
TCL_STDOUT,
TCL_STDERR,
and
TCL_ENFORCE_MODE.
If
TCL_STDIN
is set,
stdin for
the first
child in
the pipe is
the pipe
channel,
otherwise
it is the
same as the
Tcl 7.5 3
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
standard
input of
the invok-
ing pro-
cess; like-
wise for
TCL_STDOUT
and
TCL_STDERR.
If
TCL_ENFORCE_MODE
is not set,
then the
pipe can
redirect
stdio han-
dles to
override
the stdio
handles for
which
TCL_STDIN,
TCL_STDOUT
and
TCL_STDERR
have been
set. If it
is set,
then such
redirec-
tions cause
an error.
ClientData inOsFile (in) Operating
system spe-
cific han-
dle for
input from
a file. For
Unix this
is a file
descriptor,
for Windows
it is a
HANDLE,
etc.
ClientData outOsFile (in) Operating
system spe-
cific han-
dle for
output to a
file.
Tcl 7.5 4
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
int readOrWrite (in) OR-ed com-
bination of
TCL_READ-
ABLE and
TCL_WRITABLE
to indicate
which of
inOsFile
and outOs-
File con-
tains a
valid
value.
int *modePtr (out) Points at
an integer
variable
that will
receive an
OR-ed com-
bination of
TCL_READ-
ABLE and
TCL_WRITABLE
denoting
whether the
channel is
open for
reading and
writing.
Tcl_Channel channel (in) A Tcl chan-
nel for
input or
output.
Must have
been the
return
value from
a procedure
such as
Tcl_Open-
FileChan-
nel.
char *buf (in) An array of
bytes in
which to
store chan-
nel input,
or from
which to
read chan-
nel output.
Tcl 7.5 5
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
int len (in) The length
of the
input or
output.
int atEnd (in) If nonzero,
store the
input at
the end of
the input
queue, oth-
erwise
store it at
the head of
the input
queue.
int toRead (in) The number
of bytes to
read from
the chan-
nel.
Tcl_DString *lineRead (in) A pointer
to a Tcl
dynamic
string in
which to
store the
line read
from the
channel.
Must have
been ini-
tialized by
the caller.
int toWrite (in) The number
of bytes to
read from
buf and
output to
the chan-
nel.
int offset (in) How far to
move the
access
point in
the channel
at which
the next
input or
output
Tcl 7.5 6
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
operation
will be
applied,
measured in
bytes from
the posi-
tion given
by seek-
Mode. May
be either
positive or
negative.
int seekMode (in) Relative to
which point
to seek;
used with
offset to
calculate
the new
access
point for
the chan-
nel. Legal
values are
SEEK_SET,
SEEK_CUR,
and
SEEK_END.
char *optionName (in) The name of
an option
applicable
to this
channel,
such as
-blocking.
May have
any of the
values
accepted by
the fcon-
figure com-
mand.
Tcl_DString *optionValue (in) Where to
store the
value of an
option or a
list of all
options and
their val-
ues. Must
have been
Tcl 7.5 7
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
initialized
by the
caller.
char *newValue (in) New value
for the
option
given by
optionName.
_________________________________________________________________DESCRIPTION
The Tcl channel mechanism provides a device-independent
and platform-independent mechanism for performing buffered
input and output operations on a variety of file, socket,
and device types. The channel mechanism is extensible to
new channel types, by providing a low level channel driver
for the new type; the channel driver interface is
described in the manual entry for Tcl_CreateChannel. The
channel mechanism provides a buffering scheme modelled
after Unix's standard I/O, and it also allows for non-
blocking I/O on channels.
The procedures described in this manual entry comprise the
C APIs of the generic layer of the channel architecture.
For a description of the channel driver architecture and
how to implement channel drivers for new types of chan-
nels, see the manual entry for Tcl_CreateChannel.
TCL_OPENFILECHANNEL
Tcl_OpenFileChannel opens a file specified by fileName and
returns a channel handle that can be used to perform input
and output on the file. This API is modelled after the
fopen procedure of the Unix standard I/O library. The
syntax and meaning of all arguments is similar to those
given in the Tcl open command when opening a file. If an
error occurs while opening the channel, Tcl_OpenFileChan-
nel returns NULL and records a POSIX error code that can
be retrieved with Tcl_GetErrno. In addition, if interp is
non-NULL, Tcl_OpenFileChannel leaves an error message in
interp->result after any error.
The newly created channel is not registered in the sup-
plied interpreter; to register it, use Tcl_RegisterChan-
nel, described below. If one of the standard channels,
stdin, stdout or stderr was previously closed, the act of
creating the new channel also assigns it as a replacement
for the standard channel.
TCL_OPENCOMMANDCHANNEL
Tcl_OpenCommandChannel provides a C-level interface to the
Tcl 7.5 8
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
functions of the exec and open commands. It creates a
sequence of subprocesses specified by the argv and argc
arguments and returns a channel that can be used to commu-
nicate with these subprocesses. The flags argument indi-
cates what sort of communication will exist with the com-
mand pipeline.
If the TCL_STDIN flag is set then the standard input for
the first subprocess will be tied to the channel: writing
to the channel will provide input to the subprocess. If
TCL_STDIN is not set, then standard input for the first
subprocess will be the same as this application's standard
input. If TCL_STDOUT is set then standard output from the
last subprocess can be read from the channel; otherwise it
goes to this application's standard output. If TCL_STDERR
is set, standard error output for all subprocesses is
returned to the channel and results in an error when the
channel is closed; otherwise it goes to this application's
standard error. If TCL_ENFORCE_MODE is not set, then argc
and argv can redirect the stdio handles to override
TCL_STDIN, TCL_STDOUT, and TCL_STDERR; if it is set, then
it is an error for argc and argv to override stdio chan-
nels for which TCL_STDIN, TCL_STDOUT, and TCL_STDERR have
been set.
If an error occurs while opening the channel, Tcl_OpenCom-
mandChannel returns NULL and records a POSIX error code
that can be retrieved with Tcl_GetErrno. In addition,
Tcl_OpenCommandChannel leaves an error message in
interp->result if interp is not NULL.
The newly created channel is not registered in the sup-
plied interpreter; to register it, use Tcl_RegisterChan-
nel, described below. If one of the standard channels,
stdin, stdout or stderr was previously closed, the act of
creating the new channel also assigns it as a replacement
for the standard channel.
TCL_MAKEFILECHANNEL
Tcl_MakeFileChannel makes a Tcl_Channel from an existing,
platform-specific, file handle. The newly created channel
is not registered in the supplied interpreter; to register
it, use Tcl_RegisterChannel, described below. If one of
the standard channels, stdin, stdout or stderr was previ-
ously closed, the act of creating the new channel also
assigns it as a replacement for the standard channel.
TCL_GETCHANNEL
Tcl_GetChannel returns a channel given the channelName
used to create it with Tcl_CreateChannel and a pointer to
a Tcl interpreter in interp. If a channel by that name is
not registered in that interpreter, the procedure returns
Tcl 7.5 9
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
NULL. If the mode argument is not NULL, it points at an
integer variable that will receive an OR-ed combination of
TCL_READABLE and TCL_WRITABLE describing whether the chan-
nel is open for reading and writing.
TCL_REGISTERCHANNEL
Tcl_RegisterChannel adds a channel to the set of channels
accessible in interp. After this call, Tcl programs exe-
cuting in that interpreter can refer to the channel in
input or output operations using the name given in the
call to Tcl_CreateChannel. After this call, the channel
becomes the property of the interpreter, and the caller
should not call Tcl_Close for the channel; the channel
will be closed automatically when it is unregistered from
the interpreter.
Code executing outside of any Tcl interpreter can call
Tcl_RegisterChannel with interp as NULL, to indicate that
it wishes to hold a reference to this channel. Subse-
quently, the channel can be registered in a Tcl inter-
preter and it will only be closed when the matching number
of calls to Tcl_UnregisterChannel have been made. This
allows code executing outside of any interpreter to safely
hold a reference to a channel that is also registered in a
Tcl interpreter.
TCL_UNREGISTERCHANNEL
Tcl_UnregisterChannel removes a channel from the set of
channels accessible in interp. After this call, Tcl pro-
grams will no longer be able to use the channel's name to
refer to the channel in that interpreter. If this opera-
tion removed the last registration of the channel in any
interpreter, the channel is also closed and destroyed.
Code not associated with a Tcl interpreter can call
Tcl_UnregisterChannel with interp as NULL, to indicate to
Tcl that it no longer holds a reference to that channel.
If this is the last reference to the channel, it will now
be closed.
TCL_CLOSE
Tcl_Close destroys the channel channel, which must denote
a currently open channel. The channel should not be regis-
tered in any interpreter when Tcl_Close is called.
Buffered output is flushed to the channel's output device
prior to destroying the channel, and any buffered input is
discarded. If this is a blocking channel, the call does
not return until all buffered data is successfully sent to
the channel's output device. If this is a nonblocking
channel and there is buffered output that cannot be writ-
ten without blocking, the call returns immediately; output
Tcl 7.5 10
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
is flushed in the background and the channel will be
closed once all of the buffered data has been output. In
this case errors during flushing are not reported.
If the channel was closed successfully, Tcl_Close returns
TCL_OK. If an error occurs, Tcl_Close returns TCL_ERROR
and records a POSIX error code that can be retrieved with
Tcl_GetErrno. If the channel is being closed syn-
chronously and an error occurs during closing of the chan-
nel and interp is not NULL, an error message is left in
interp->result.
Note: it is not safe to call Tcl_Close on a channel that
has been registered using Tcl_RegisterChannel; see the
documentation for Tcl_RegisterChannel, above, for details.
If the channel has ever been given as the chan argument in
a call to Tcl_RegisterChannel, you should instead use
Tcl_UnregisterChannel, which will internally call
Tcl_Close when all calls to Tcl_RegisterChannel have been
matched by corresponding calls to Tcl_UnregisterChannel.
TCL_READ
Tcl_Read consumes up to toRead bytes of data from channel
and stores it at buf. The return value of Tcl_Read is the
number of characters written at buf. The buffer produced
by Tcl_Read is not NULL terminated. Its contents are valid
from the zeroth position up to and excluding the position
indicated by the return value. If an error occurs, the
return value is -1 and Tcl_Read records a POSIX error code
that can be retrieved with Tcl_GetErrno.
The return value may be smaller than the value of toRead,
indicating that less data than requested was available,
also called a short read. In blocking mode, this can only
happen on an end-of-file. In nonblocking mode, a short
read can also occur if there is not enough input currently
available: Tcl_Read returns a short count rather than
waiting for more data.
If the channel is in blocking mode, a return value of zero
indicates an end of file condition. If the channel is in
nonblocking mode, a return value of zero indicates either
that no input is currently available or an end of file
condition. Use Tcl_Eof and Tcl_InputBlocked to tell which
of these conditions actually occurred.
Tcl_Read translates platform-specific end-of-line repre-
sentations into the canonical \n internal representation
according to the current end-of-line recognition mode.
End-of-line recognition and the various platform-specific
modes are described in the manual entry for the Tcl fcon-
figure command.
Tcl 7.5 11
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)TCL_GETS
Tcl_Gets reads a line of input from a channel and appends
all of the characters of the line except for the terminat-
ing end-of-line character(s) to the dynamic string given
by dsPtr. The end-of-line character(s) are read and dis-
carded.
If a line was successfully read, the return value is
greater than or equal to zero, and it indicates the number
of characters stored in the dynamic string. If an error
occurs, Tcl_Gets returns -1 and records a POSIX error code
that can be retrieved with Tcl_GetErrno. Tcl_Gets also
returns -1 if the end of the file is reached; the Tcl_Eof
procedure can be used to distinguish an error from an end-
of-file condition.
If the channel is in nonblocking mode, the return value
can also be -1 if no data was available or the data that
was available did not contain an end-of-line character.
When -1 is returned, the Tcl_InputBlocked procedure may be
invoked to determine if the channel is blocked because of
input unavailability.
TCL_WRITE
Tcl_Write accepts toWrite bytes of data at buf for output
on channel. This data may not appear on the output device
immediately. If the data should appear immediately, call
Tcl_Flush after the call to Tcl_Write, or set the -buffer-
ing option on the channel to none. If you wish the data to
appear as soon as an end of line is accepted for output,
set the -buffering option on the channel to line mode.
The toWrite argument specifies how many bytes of data are
provided in the buf argument. If it is negative, Tcl_Write
expects the data to be NULL terminated and it outputs
everything up to the NULL.
The return value of Tcl_Write is a count of how many char-
acters were accepted for output to the channel. This is
either equal to toWrite or -1 to indicate that an error
occurred. If an error occurs, Tcl_Write also records a
POSIX error code that may be retrieved with Tcl_GetErrno.
Newline characters in the output data are translated to
platform-specific end-of-line sequences according to the
-translation option for the channel.
TCL_FLUSH
Tcl_Flush causes all of the buffered output data for chan-
nel to be written to its underlying file or device as soon
as possible. If the channel is in blocking mode, the call
does not return until all the buffered data has been sent
Tcl 7.5 12
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
to the channel or some error occurred. The call returns
immediately if the channel is nonblocking; it starts a
background flush that will write the buffered data to the
channel eventually, as fast as the channel is able to
absorb it.
The return value is normally TCL_OK. If an error occurs,
Tcl_Flush returns TCL_ERROR and records a POSIX error code
that can be retrieved with Tcl_GetErrno.
TCL_SEEK
Tcl_Seek moves the access point in channel where subse-
quent data will be read or written. Buffered output is
flushed to the channel and buffered input is discarded,
prior to the seek operation.
Tcl_Seek normally returns the new access point. If an
error occurs, Tcl_Seek returns -1 and records a POSIX
error code that can be retrieved with Tcl_GetErrno. After
an error, the access point may or may not have been moved.
TCL_TELLTcl_Tell returns the current access point for a channel.
The returned value is -1 if the channel does not support
seeking.
TCL_GETCHANNELOPTION
Tcl_GetChannelOption retrieves, in dsPtr, the value of one
of the options currently in effect for a channel, or a
list of all options and their values. The channel argu-
ment identifies the channel for which to query an option
or retrieve all options and their values. If optionName
is not NULL, it is the name of the option to query; the
option's value is copied to the Tcl dynamic string denoted
by optionValue. If optionName is NULL, the function stores
an alternating list of option names and their values in
optionValue, using a series of calls to Tcl_DStringAppen-
dElement. The various preexisting options and their possi-
ble values are described in the manual entry for the Tcl
fconfigure command. Other options can be added by each
channel type. These channel type specific options are
described in the manual entry for the Tcl command that
creates a channel of that type; for example, the addi-
tional options for TCP based channels are described in the
manual entry for the Tcl socket command. The procedure
normally returns TCL_OK. If an error occurs, it returns
TCL_ERROR and calls Tcl_SetErrno to store an appropriate
POSIX error code.
Tcl 7.5 13
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)TCL_SETCHANNELOPTION
Tcl_SetChannelOption sets a new value for an option on
channel. OptionName is the option to set and newValue is
the value to set. The procedure normally returns TCL_OK.
If an error occurs, it returns TCL_ERROR; in addition, if
interp is non-NULL, Tcl_SetChannelOption leaves an error
message in interp->result.
TCL_EOF
Tcl_Eof returns a nonzero value if channel encountered an
end of file during the last input operation.
TCL_INPUTBLOCKED
Tcl_InputBlocked returns a nonzero value if channel is in
nonblocking mode and the last input operation returned
less data than requested because there was insufficient
data available. The call always returns zero if the chan-
nel is in blocking mode.
TCL_INPUTBUFFERED
Tcl_InputBuffered returns the number of bytes of input
currently buffered in the internal buffers for a channel.
If the channel is not open for reading, this function
always returns zero.
SEE ALSODString(3), fconfigure(n), filename(n), fopen(2), Tcl_Cre-
ateChannel(3)KEYWORDS
access point, blocking, buffered I/O, channel, channel
driver, end of file, flush, input, nonblocking, output,
read, seek, write
Tcl 7.5 14
