Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
_________________________________________________________________
NAME
Tcl_OpenFileChannel, Tcl_OpenCommandChannel,
Tcl_MakeFileChannel, Tcl_GetChannel, Tcl_RegisterChannel,
Tcl_UnregisterChannel, Tcl_Close, Tcl_Read, Tcl_Gets,
Tcl_Write, Tcl_Flush, Tcl_Seek, Tcl_Tell, Tcl_Eof,
Tcl_InputBlocked, Tcl_InputBuffered, Tcl_GetChannelOption,
Tcl_SetChannelOption - buffered I/O facilities using
channels
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(handle, 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_GetsObj(channel, lineObjPtr)
int
Tcl_Write(channel, buf, toWrite)
int
Tcl_Flush(channel)
Page 1 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
int
Tcl_Seek(channel, offset, seekMode)
int
Tcl_Tell(channel)
int
Tcl_GetChannelOption(interp, 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
channel
registered 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
command. For
Tcl_OpenCommandChannel,
may be NULL.
int permissions (in) POSIX-style
permission
flags such as
Page 2 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
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.
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
Page 3 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
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 Windows |
it is a |
HANDLE. |
int readOrWrite (in) ||
OR-ed |
combination |
of |
TCL_READABLE |
and |
TCL_WRITABLE |
to indicate |
what |
operations |
are valid on |
handle.
Page 4 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
int *modePtr (out) Points at an
integer
variable that
will receive
an OR-ed
combination
of
TCL_READABLE
and
TCL_WRITABLE
denoting
whether the
channel is
open for
reading and
writing.
Tcl_Channel channel (in) A Tcl channel
for input or
output. Must
have been the
return value
from a
procedure
such as
Tcl_OpenFileChannel.
char *buf (in) An array of
bytes in
which to
store channel
input, or
from which to
read channel
output.
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,
otherwise
store it at
the head of
the input
queue.
int toRead (in) The number of
Page 5 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
bytes to read
from the
channel.
Tcl_DString *lineRead (in) 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.
Tcl_Obj *linePtrObj (in) A pointer to
a Tcl object
in which to
store the
line read
from the
channel. The
line read
will be
appended to
the current
value of the
object.
int toWrite (in) The number of
bytes to read
from buf and
output to the
channel.
int offset (in) How far to
move the
access point
in the
channel at
which the
next input or
Page 6 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
output
operation
will be
applied,
measured in
bytes from
the position
given by
seekMode.
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.
char *optionName (in) The name of
an option
applicable to
this channel,
such as
-blocking.
May have any
of the values
accepted by
the
fconfigure
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
initialized
by the
caller.
Page 7 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
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 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 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_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-
>result after any error.
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
Page 8 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
communicate with these subprocesses. The flags argument
indicates what sort of communication will exist with the
command 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 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
interp->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 mode argument is not NULL, it points at an integer
variable that will receive an OR-ed combination of
Page 9 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
TCL_READABLE and TCL_WRITABLE describing whether the channel
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
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_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
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 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_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
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
Page 10 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
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 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
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.
Page 11 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
TCL_GETS AND TCL_GETSOBJ
Tcl_Gets reads a line of input from a channel and appends
all of the characters of the line except for the terminating
end-of-line character(s) to the dynamic string given by
dsPtr. 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 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_GetsObj is the same as Tcl_Gets except the resulting
characters are appended to a Tcl object lineObjPtr rather
than a dynamic string.
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 -buffering
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
characters 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
Page 12 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
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 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 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_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 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
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 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 additional
options for TCP based channels are described in the manual
entry for the Tcl socket command. The procedure normally
Page 13 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
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 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 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.
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_MakeFileChannel. Other channel types may return a |
different type of handle on Windows platforms. On the |
Macintosh platform, the handle is a file reference number as |
returned from HOpenDF.
SEE ALSO
DString(3), fconfigure(n), filename(n), fopen(2),
Tcl_CreateChannel(3)
KEYWORDS
Page 14 (printed 2/19/99)
Tcl_OpenFileChannel(3) Tcl (8.0) Tcl_OpenFileChannel(3)
access point, blocking, buffered I/O, channel, channel
driver, end of file, flush, input, nonblocking, output,
read, seek, write
Page 15 (printed 2/19/99)
