Tcl_OpenFileChannel(3) Tcl Library Procedures Tcl_OpenFileChannel(3)______________________________________________________________________________NAME
Tcl_OpenFileChannel, Tcl_OpenCommandChannel, Tcl_MakeFileChannel,
Tcl_GetChannel, Tcl_GetChannelNames, Tcl_GetChannelNamesEx, Tcl_Regis‐
terChannel, Tcl_UnregisterChannel, Tcl_DetachChannel, Tcl_IsStandard‐
Channel, Tcl_Close, Tcl_ReadChars, Tcl_Read, Tcl_GetsObj, Tcl_Gets,
Tcl_WriteObj, Tcl_WriteChars, Tcl_Write, Tcl_Flush, Tcl_Seek, Tcl_Tell,
Tcl_TruncateChannel, Tcl_GetChannelOption, Tcl_SetChannelOption,
Tcl_Eof, Tcl_InputBlocked, Tcl_InputBuffered, Tcl_OutputBuffered,
Tcl_Ungets, Tcl_ReadRaw, Tcl_WriteRaw - buffered I/O facilities using
channels
SYNOPSIS
#include <tcl.h>
Tcl_Channel
Tcl_OpenFileChannel(interp, fileName, mode, permissions)
Tcl_Channel
Tcl_OpenCommandChannel(interp, argc, argv, flags)
Tcl_Channel
Tcl_MakeFileChannel(handle, readOrWrite)
Tcl_Channel
Tcl_GetChannel(interp, channelName, modePtr)
int
Tcl_GetChannelNames(interp)
int
Tcl_GetChannelNamesEx(interp, pattern)
void
Tcl_RegisterChannel(interp, channel)
int
Tcl_UnregisterChannel(interp, channel)
int
Tcl_DetachChannel(interp, channel)
int
Tcl_IsStandardChannel(channel)
int
Tcl_Close(interp, channel)
int
Tcl_ReadChars(channel, readObjPtr, charsToRead, appendFlag)
int
Tcl_Read(channel, readBuf, bytesToRead)
int
Tcl_GetsObj(channel, lineObjPtr)
int
Tcl_Gets(channel, lineRead)
int
Tcl_Ungets(channel, input, inputLen, addAtEnd)
int
Tcl_WriteObj(channel, writeObjPtr)
int
Tcl_WriteChars(channel, charBuf, bytesToWrite)
int
Tcl_Write(channel, byteBuf, bytesToWrite)
int
Tcl_ReadRaw(channel, readBuf, bytesToRead)
int
Tcl_WriteRaw(channel, byteBuf, bytesToWrite)
int
Tcl_Eof(channel)
int
Tcl_Flush(channel)
int
Tcl_InputBlocked(channel)
int
Tcl_InputBuffered(channel)
int
Tcl_OutputBuffered(channel)
Tcl_WideInt
Tcl_Seek(channel, offset, seekMode)
Tcl_WideInt
Tcl_Tell(channel)
int
Tcl_TruncateChannel(channel, length)
int
Tcl_GetChannelOption(interp, channel, optionName, optionValue)
int
Tcl_SetChannelOption(interp, channel, optionName, newValue)
ARGUMENTS
Tcl_Interp *interp (in) Used for error reporting and to
look up a channel registered in
it.
const char *fileName (in) The name of a local or network
file.
const 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.
int permissions (in) POSIX-style permission flags
such as 0644. If a new file is
created, these permissions will
be set on the created file.
int argc (in) The number of elements in argv.
const char **argv (in) Arguments for constructing a
command pipeline. These values
have the same meaning as the
non-switch arguments to the Tcl
exec command.
int flags (in) Specifies the disposition of the
stdio handles in pipeline: OR-ed
combination 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 standard input of
the invoking process; likewise
for TCL_STDOUT and TCL_STDERR.
If TCL_ENFORCE_MODE is not set,
then the pipe can redirect stdio
handles to override the stdio
handles for which TCL_STDIN,
TCL_STDOUT and TCL_STDERR have
been set. If it is set, then
such redirections cause an
error.
ClientData handle (in) Operating system specific handle
for I/O to a file. For Unix this
is a file descriptor, for Win‐
dows it is a HANDLE.
int readOrWrite (in) OR-ed combination of TCL_READ‐
ABLE and TCL_WRITABLE to indi‐
cate what operations are valid
on handle.
const char *channelName (in) The name of the channel.
int *modePtr (out) Points at an integer variable
that will receive an OR-ed com‐
bination of TCL_READABLE and
TCL_WRITABLE denoting whether
the channel is open for reading
and writing.
const char *pattern (in) The pattern to match on, passed
to Tcl_StringMatch, or NULL.
Tcl_Channel channel (in) A Tcl channel for input or out‐
put. Must have been the return
value from a procedure such as
Tcl_OpenFileChannel.
Tcl_Obj *readObjPtr (in/out) A pointer to a Tcl value in
which to store the characters
read from the channel.
int charsToRead (in) The number of characters to read
from the channel. If the chan‐
nel's encoding is binary, this
is equivalent to the number of
bytes to read from the channel.
int appendFlag (in) If non-zero, data read from the
channel will be appended to the
value. Otherwise, the data will
replace the existing contents of
the value.
char *readBuf (out) A buffer in which to store the
bytes read from the channel.
int bytesToRead (in) The number of bytes to read from
the channel. The buffer readBuf
must be large enough to hold
this many bytes.
Tcl_Obj *lineObjPtr (in/out) A pointer to a Tcl value in
which to store the line read
from the channel. The line read
will be appended to the current
value of the value.
Tcl_DString *lineRead (in/out) A pointer to a Tcl dynamic
string in which to store the
line read from the channel.
Must have been initialized by
the caller. The line read will
be appended to any data already
in the dynamic string.
const char *input (in) The input to add to a channel
buffer.
int inputLen (in) Length of the input
int addAtEnd (in) Flag indicating whether the
input should be added to the end
or beginning of the channel buf‐
fer.
Tcl_Obj *writeObjPtr (in) A pointer to a Tcl value whose
contents will be output to the
channel.
const char *charBuf (in) A buffer containing the charac‐
ters to output to the channel.
const char *byteBuf (in) A buffer containing the bytes to
output to the channel.
int bytesToWrite (in) The number of bytes to consume
from charBuf or byteBuf and out‐
put to the channel.
Tcl_WideInt offset (in) How far to move the access point
in the channel at which the next
input or output operation will
be applied, measured in bytes
from the position 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
channel. Legal values are
SEEK_SET, SEEK_CUR, and
SEEK_END.
Tcl_WideInt length (in) The (non-negative) length to
truncate the channel the channel
to.
const char *optionName (in) The name of an option applicable
to this channel, such as -block‐
ing. May have any of the values
accepted by the fconfigure com‐
mand.
Tcl_DString *optionValue (in) Where to store the value of an
option or a list of all options
and their values. Must have been
initialized by the caller.
const 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 opera‐
tions 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 mecha‐
nism provides a buffering scheme modeled after Unix's standard I/O, and
it also allows for nonblocking 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 channels, 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 modeled after the fopen procedure of the Unix stan‐
dard 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_OpenFileChannel 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's result after any error. As of Tcl
8.4, the value-based API Tcl_FSOpenFileChannel should be used in pref‐
erence to Tcl_OpenFileChannel wherever possible.
The newly created channel is not registered in the supplied inter‐
preter; to register it, use Tcl_RegisterChannel, 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 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 communicate with these subprocesses. The flags argument
indicates what sort of communication will exist with the command pipe‐
line.
If the TCL_STDIN flag is set then the standard input for the first sub‐
process will be tied to the channel: writing to the channel will pro‐
vide 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 applica‐
tion'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 channels for which TCL_STDIN, TCL_STDOUT, and TCL_STDERR
have been set.
If an error occurs while opening the channel, Tcl_OpenCommandChannel
returns NULL and records a POSIX error code that can be retrieved with
Tcl_GetErrno. In addition, Tcl_OpenCommandChannel leaves an error mes‐
sage in the interpreter's result if interp is not NULL.
The newly created channel is not registered in the supplied inter‐
preter; to register it, use Tcl_RegisterChannel, 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-spe‐
cific, 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 previously 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 NULL. If the modePtr 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 channel is open
for reading and writing.
Tcl_GetChannelNames and Tcl_GetChannelNamesEx write the names of the
registered channels to the interpreter's result as a list value.
Tcl_GetChannelNamesEx will filter these names according to the pattern.
If pattern is NULL, then it will not do any filtering. The return
value is TCL_OK if no errors occurred writing to the result, otherwise
it is TCL_ERROR, and the error message is left in the interpreter's
result.
TCL_REGISTERCHANNEL
Tcl_RegisterChannel adds a channel to the set of channels accessible in
interp. After this call, Tcl programs executing 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_Register‐
Channel with interp as NULL, to indicate that it wishes to hold a ref‐
erence to this channel. Subsequently, the channel can be registered in
a Tcl interpreter 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.
This procedure interacts with the code managing the standard channels.
If no standard channels were initialized before the first call to
Tcl_RegisterChannel, they will get initialized by that call. See
Tcl_StandardChannels for a general treatise about standard channels and
the behavior of the Tcl library with regard to them.
TCL_UNREGISTERCHANNEL
Tcl_UnregisterChannel removes a channel from the set of channels acces‐
sible in interp. After this call, Tcl programs will no longer be able
to use the channel's name to refer to the channel in that interpreter.
If this operation 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_UnregisterChan‐
nel 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 chan‐
nel, it will now be closed. Tcl_UnregisterChannel is very similar to
Tcl_DetachChannel except that it will also close the channel if no fur‐
ther references to it exist.
TCL_DETACHCHANNEL
Tcl_DetachChannel removes a channel from the set of channels accessible
in interp. After this call, Tcl programs will no longer be able to use
the channel's name to refer to the channel in that interpreter. Beyond
that, this command has no further effect. It cannot be used on the
standard channels (stdout, stderr, stdin), and will return TCL_ERROR if
passed one of those channels.
Code not associated with a Tcl interpreter can call Tcl_DetachChannel
with interp as NULL, to indicate to Tcl that it no longer holds a ref‐
erence to that channel. If this is the last reference to the channel,
unlike Tcl_UnregisterChannel, it will not be closed.
TCL_ISSTANDARDCHANNEL
Tcl_IsStandardChannel tests whether a channel is one of the three stan‐
dard channels, stdin, stdout or stderr. If so, it returns 1, otherwise
0.
No attempt is made to check whether the given channel or the standard
channels are initialized or otherwise valid.
TCL_CLOSETcl_Close destroys the channel channel, which must denote a currently
open channel. The channel should not be registered 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 written without blocking, the call returns immediately;
output 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 synchronously and an error occurs during closing of the channel
and interp is not NULL, an error message is left in the interpreter's
result.
Note: it is not safe to call Tcl_Close on a channel that has been reg‐
istered using Tcl_RegisterChannel; see the documentation for Tcl_Regis‐
terChannel, 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_READCHARS AND TCL_READ
Tcl_ReadChars consumes bytes from channel, converting the bytes to
UTF-8 based on the channel's encoding and storing the produced data in
readObjPtr's string representation. The return value of Tcl_ReadChars
is the number of characters, up to charsToRead, that were stored in
readObjPtr. If an error occurs while reading, the return value is -1
and Tcl_ReadChars records a POSIX error code that can be retrieved with
Tcl_GetErrno.
Setting charsToRead to -1 will cause the command to read all characters
currently available (non-blocking) or everything until eof (blocking
mode).
The return value may be smaller than the value to read, indicating that
less data than requested was available. This is called a short read.
In blocking mode, this can only happen on an end-of-file. In nonblock‐
ing mode, a short read can also occur if there is not enough input cur‐
rently available: Tcl_ReadChars 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_ReadChars translates the various end-of-line representations 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
fconfigure command.
As a performance optimization, when reading from a channel with the
encoding binary, the bytes are not converted to UTF-8 as they are read.
Instead, they are stored in readObjPtr's internal representation as a
byte-array value. The string representation of this value will only be
constructed if it is needed (e.g., because of a call to Tcl_Get‐
StringFromObj). In this way, byte-oriented data can be read from a
channel, manipulated by calling Tcl_GetByteArrayFromObj and related
functions, and then written to a channel without the expense of ever
converting to or from UTF-8.
Tcl_Read is similar to Tcl_ReadChars, except that it does not do encod‐
ing conversions, regardless of the channel's encoding. It is depre‐
cated and exists for backwards compatibility with non-internationalized
Tcl extensions. It consumes bytes from channel and stores them in
readBuf, performing end-of-line translations on the way. The return
value of Tcl_Read is the number of bytes, up to bytesToRead, written in
readBuf. 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.
Tcl_ReadRaw is the same as Tcl_Read but does not compensate for stack‐
ing. While Tcl_Read (and the other functions in the API) always get
their data from the topmost channel in the stack the supplied channel
is part of, Tcl_ReadRaw does not. Thus this function is only usable for
transformational channel drivers, i.e. drivers used in the middle of a
stack of channels, to move data from the channel below into the trans‐
formation.
TCL_GETSOBJ AND TCL_GETS
Tcl_GetsObj consumes bytes from channel, converting the bytes to UTF-8
based on the channel's encoding, until a full line of input has been
seen. If the channel's encoding is binary, each byte read from the
channel is treated as an individual Unicode character. All of the
characters of the line except for the terminating end-of-line charac‐
ter(s) are appended to lineObjPtr's string representation. The end-of-
line character(s) are read and discarded.
If a line was successfully read, the return value is greater than or
equal to zero and indicates the number of bytes stored in lineObjPtr.
If an error occurs, Tcl_GetsObj returns -1 and records a POSIX error
code that can be retrieved with Tcl_GetErrno. Tcl_GetsObj 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_Gets is the same as Tcl_GetsObj except the resulting characters are
appended to the dynamic string given by lineRead rather than a Tcl
value.
TCL_UNGETS
Tcl_Ungets is used to add data to the input queue of a channel, at
either the head or tail of the queue. The pointer input points to the
data that is to be added. The length of the input to add is given by
inputLen. A non-zero value of addAtEnd indicates that the data is to
be added at the end of queue; otherwise it will be added at the head of
the queue. If channel has a “sticky” EOF set, no data will be added to
the input queue. Tcl_Ungets returns inputLen or -1 if an error occurs.
TCL_WRITECHARS, TCL_WRITEOBJ, AND TCL_WRITE
Tcl_WriteChars accepts bytesToWrite bytes of character data at charBuf.
The UTF-8 characters in the buffer are converted to the channel's
encoding and queued for output to channel. If bytesToWrite is nega‐
tive, Tcl_WriteChars expects charBuf to be null-terminated and it out‐
puts everything up to the null.
Data queued for output may not appear on the output device immediately,
due to internal buffering. If the data should appear immediately, call
Tcl_Flush after the call to Tcl_WriteChars, or set the -buffering
option on the channel to none. If you wish the data to appear as soon
as a complete line is accepted for output, set the -buffering option on
the channel to line mode.
The return value of Tcl_WriteChars is a count of how many bytes were
accepted for output to the channel. This is either greater than zero
to indicate success or -1 to indicate that an error occurred. If an
error occurs, Tcl_WriteChars records a POSIX error code that may be
retrieved with Tcl_GetErrno.
Newline characters in the output data are translated to platform-spe‐
cific end-of-line sequences according to the -translation option for
the channel. This is done even if the channel has no encoding.
Tcl_WriteObj is similar to Tcl_WriteChars except it accepts a Tcl value
whose contents will be output to the channel. The UTF-8 characters in
writeObjPtr's string representation are converted to the channel's
encoding and queued for output to channel. As a performance optimiza‐
tion, when writing to a channel with the encoding binary, UTF-8 charac‐
ters are not converted as they are written. Instead, the bytes in
writeObjPtr's internal representation as a byte-array value are written
to the channel. The byte-array representation of the value will be
constructed if it is needed. In this way, byte-oriented data can be
read from a channel, manipulated by calling Tcl_GetByteArrayFromObj and
related functions, and then written to a channel without the expense of
ever converting to or from UTF-8.
Tcl_Write is similar to Tcl_WriteChars except that it does not do
encoding conversions, regardless of the channel's encoding. It is dep‐
recated and exists for backwards compatibility with non-international‐
ized Tcl extensions. It accepts bytesToWrite bytes of data at byteBuf
and queues them for output to channel. If bytesToWrite is negative,
Tcl_Write expects byteBuf to be null-terminated and it outputs every‐
thing up to the null.
Tcl_WriteRaw is the same as Tcl_Write but does not compensate for
stacking. While Tcl_Write (and the other functions in the API) always
feed their input to the topmost channel in the stack the supplied chan‐
nel is part of, Tcl_WriteRaw does not. Thus this function is only
usable for transformational channel drivers, i.e. drivers used in the
middle of a stack of channels, to move data from the transformation
into the channel below it.
TCL_FLUSH
Tcl_Flush causes all of the buffered output data for channel 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 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 even‐
tually, 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 subsequent 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_TELL
Tcl_Tell returns the current access point for a channel. The returned
value is -1 if the channel does not support seeking.
TCL_TRUNCATECHANNEL
Tcl_TruncateChannel truncates the file underlying channel to a given
length of bytes. It returns TCL_OK if the operation succeeded, and
TCL_ERROR otherwise.
TCL_GETCHANNELOPTION
Tcl_GetChannelOption retrieves, in optionValue, the value of one of the
options currently in effect for a channel, or a list of all options and
their values. The channel argument identifies the channel for which to
query an option or retrieve all options and their values. If option‐
Name 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_DStringAppendElement. The various preexisting options and their
possible values are described in the manual entry for the Tcl fconfig‐
ure 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_SETCHANNELOPTION
Tcl_SetChannelOption sets a new value newValue for an option optionName
on channel. 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 the interpreter's
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 channel 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.
TCL_OUTPUTBUFFERED
Tcl_OutputBuffered returns the number of bytes of output currently
buffered in the internal buffers for a channel. If the channel is not
open for writing, this function always returns zero.
PLATFORM ISSUES
The handles returned from Tcl_GetChannelHandle depend on the platform
and the channel type. On Unix platforms, the handle is always a Unix
file descriptor as returned from the open system call. On Windows
platforms, the handle is a file HANDLE when the channel was created
with Tcl_OpenFileChannel, Tcl_OpenCommandChannel, or Tcl_MakeFileChan‐
nel. Other channel types may return a different type of handle on Win‐
dows platforms.
SEE ALSODString(3), fconfigure(n), filename(n), fopen(3), Tcl_CreateChannel(3)KEYWORDS
access point, blocking, buffered I/O, channel, channel driver, end of
file, flush, input, nonblocking, output, read, seek, write
Tcl 8.3 Tcl_OpenFileChannel(3)
