Tcl_MakeFileChannel(3tcl)
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
_________________________________________________________________
NAME
Tcl_OpenFileChannel, Tcl_OpenCommandChannel,
Tcl_MakeFileChannel, Tcl_GetChannel, Tcl_GetChannelNames,
Tcl_GetChannelNamesEx, Tcl_RegisterChannel,
Tcl_UnregisterChannel, Tcl_DetachChannel,
Tcl_IsStandardChannel, 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)
Tcl Last change: 8.3 1
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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 Last change: 8.3 2
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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 command.
int permissions (in) POSIX-style permis-
sion 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 ele-
ments in argv.
const char **argv (in) Arguments for con-
structing a command
pipeline. These
values have the same
meaning as the non-
switch arguments to
the Tcl exec command.
int flags (in) Specifies the dispo-
sition of the stdio
handles in pipeline:
OR-ed combination of
TCL_STDIN,
TCL_STDOUT,
TCL_STDERR, and
Tcl Last change: 8.3 3
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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_READABLE and
TCL_WRITABLE to indi-
cate what operations
are valid on handle.
const char *channelName (in) The name of the chan-
nel.
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 Last change: 8.3 4
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
Tcl_StringMatch, or
NULL.
Tcl_Channel channel (in) A Tcl channel for
input or output.
Must have been the
return value from a
procedure such as
Tcl_OpenFileChannel.
Tcl_Obj *readObjPtr (in/out) A pointer to a Tcl
Object in which to
store the characters
read from the chan-
nel.
int charsToRead (in) The number of charac-
ters to read from the
channel. If the
channel's encoding is
binary, this is
equivalent to the
number of bytes to
read from the chan-
nel.
int appendFlag (in) If non-zero, data
read from the channel
will be appended to
the object. Other-
wise, the data will
replace the existing
contents of the
object.
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
object in which to
store the line read
from the channel.
The line read will be
appended to the
Tcl Last change: 8.3 5
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
current value of the
object.
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
buffer.
Tcl_Obj *writeObjPtr (in) A pointer to a Tcl
Object whose contents
will be output to the
channel.
const char *charBuf (in) A buffer containing
the characters to
output to the chan-
nel.
const char *byteBuf (in) A buffer containing
the bytes to output
to the channel.
int bytesToWrite (in) The number of bytes
to consume from char-
Buf or byteBuf and
output to the chan-
nel.
Tcl_WideInt offset (in) How far to move the
access point in the
channel at which the
next input or output
operation will be
Tcl Last change: 8.3 6
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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 calcu-
late the new access
point for the chan-
nel. Legal values are
SEEK_SET, SEEK_CUR,
and SEEK_END.
Tcl_WideInt length (in) The (non-negative)
length to truncate
the channel the chan-
nel to.
const 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 command.
Tcl_DString *optionValue (in) Where to store the
value of an option or
a list of all options
and their values.
Must have been ini-
tialized 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 operations on a variety of file, socket, and dev-
ice types. The channel mechanism is extensible to new chan-
nel 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 modeled after Unix's standard
I/O, and it also allows for nonblocking I/O on channels.
Tcl Last change: 8.3 7
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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 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_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 object-based API
Tcl_FSOpenFileChannel should be used in preference to
Tcl_OpenFileChannel wherever possible.
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_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 communi-
cate 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 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 subpro-
cess can be read from the channel; otherwise it goes to this
application's standard output. If TCL_STDERR is set, stan-
dard 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 Last change: 8.3 8
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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 message in
the interpreter's result if interp is not NULL.
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_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 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 object. 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 execut-
ing in that interpreter can refer to the channel in input or
Tcl Last change: 8.3 9
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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. 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 exe-
cuting 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 ini-
tialized by that call. See Tcl_StandardChannels for a gen-
eral treatise about standard channels and the behaviour of
the Tcl library with regard to them.
TCL_UNREGISTERCHANNEL
Tcl_UnregisterChannel 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. 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_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_UnregisterChannel is very similar to
Tcl_DetachChannel except that it will also close the channel
if no further 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 chan-
nels (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 reference to that channel. If this
Tcl Last change: 8.3 10
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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 standard 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_CLOSE
Tcl_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 destroy-
ing 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 out-
put 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 back-
ground and the channel will be closed once all of the buf-
fered 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 registered using Tcl_RegisterChannel; see the documen-
tation 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_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 charac-
ters, up to charsToRead, that were stored in readObjPtr. If
Tcl Last change: 8.3 11
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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 nonblocking mode, a short
read can also occur if there is not enough input currently
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 con-
dition. Use Tcl_Eof and Tcl_InputBlocked to tell which of
these conditions actually occurred.
Tcl_ReadChars translates the various end-of-line representa-
tions into the canonical \n internal representation accord-
ing 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 com-
mand.
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 object.
The string representation of this object will only be con-
structed if it is needed (e.g., because of a call to
Tcl_GetStringFromObj). 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 encoding conversions, regardless of the channel's
encoding. It is deprecated and exists for backwards compa-
tibility with non-internationalized Tcl extensions. It con-
sumes bytes from channel and stores them in readBuf, per-
forming 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
Tcl Last change: 8.3 12
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
return value.
Tcl_ReadRaw is the same as Tcl_Read but does not compensate
for stacking. 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 chan-
nel drivers, i.e. drivers used in the middle of a stack of
channels, to move data from the channel below into the
transformation.
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 character(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 una-
vailability.
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 object.
TCL_UNGETS
Tcl_Ungets is used to add data to the input queue of a chan-
nel, 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 Last change: 8.3 13
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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 con-
verted to the channel's encoding and queued for output to
channel. If bytesToWrite is negative, Tcl_WriteChars
expects charBuf to be null-terminated and it outputs every-
thing 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 com-
plete 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 indi-
cate 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-specific 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 object 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 out-
put to channel. As a performance optimization, when writing
to a channel with the encoding binary, UTF-8 characters are
not converted as they are written. Instead, the bytes in
writeObjPtr's internal representation as a byte-array object
are written to the channel. The byte-array representation
of the object will be constructed if it is needed. In this
way, byte-oriented data can be read from a channel, manipu-
lated by calling Tcl_GetByteArrayFromObj and related func-
tions, 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 deprecated and exists for backwards compa-
tibility with non-internationalized 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 out-
puts everything up to the null.
Tcl Last change: 8.3 14
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
Tcl_WriteRaw is the same as Tcl_Write but does not compen-
sate 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 channel is part of, Tcl_WriteRaw
does not. Thus this function is only usable for transforma-
tional 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 immedi-
ately 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 seek-
ing.
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
Tcl Last change: 8.3 15
Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
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 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 option-
Value. If optionName is NULL, the function stores an alter-
nating 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 fconfigure com-
mand. 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 additional 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 addi-
tion, 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
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Tcl_OpenFileChannel(3)Tcl Library ProcedureTcl_OpenFileChannel(3)
returns zero.
PLATFORM ISSUES
The handles returned from Tcl_GetChannelHandle depend on the
platform and the channel type. On Unix platforms, the han-
dle 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_MakeFileChannel. Other channel types may return a dif-
ferent type of handle on Windows platforms.
SEE ALSO
DString(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
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