openfilechnl.3

tcl是工具命令语言

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 \fBTcl_CreateChannel\fR. The
channel mechanism provides a buffering scheme modeled after
Unix's standard I/O, and it also allows for nonblocking I/O on
channels.
.PP
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 \fBTcl_CreateChannel\fR.

.SH TCL_OPENFILECHANNEL
.PP
\fBTcl_OpenFileChannel\fR opens a file specified by \fIfileName\fR and
returns a channel handle that can be used to perform input and output on
the file. This API is modeled after the \fBfopen\fR procedure of
the Unix standard I/O library.
The syntax and meaning of all arguments is similar to those
given in the Tcl \fBopen\fR command when opening a file.
If an error occurs while opening the channel, \fBTcl_OpenFileChannel\fR
returns NULL and records a POSIX error code that can be
retrieved with \fBTcl_GetErrno\fR.
In addition, if \fIinterp\fR is non-NULL, \fBTcl_OpenFileChannel\fR
leaves an error message in \fIinterp\fR's result after any error.  
As of Tcl 8.4, the object-based API \fBTcl_FSOpenFileChannel\fR should 
be used in preference to \fBTcl_OpenFileChannel\fR wherever possible.
.PP

.PP
The newly created channel is not registered in the supplied interpreter; to
register it, use \fBTcl_RegisterChannel\fR, described below.
If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was
previously closed, the act of creating the new channel also assigns it as a
replacement for the standard channel.

.SH TCL_OPENCOMMANDCHANNEL
.PP
\fBTcl_OpenCommandChannel\fR provides a C-level interface to the
functions of the \fBexec\fR and \fBopen\fR commands.
It creates a sequence of subprocesses specified
by the \fIargv\fR and \fIargc\fR arguments and returns a channel that can
be used to communicate with these subprocesses.
The \fIflags\fR argument indicates what sort of communication will
exist with the command pipeline.
.PP
If the \fBTCL_STDIN\fR 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 \fBTCL_STDIN\fR is not set,
then standard input for the first subprocess will be the same as this
application's standard input.  If \fBTCL_STDOUT\fR 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
\fBTCL_STDERR\fR 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
\fBTCL_ENFORCE_MODE\fR is not set, then \fIargc\fR and \fIargv\fR can
redirect the stdio handles to override \fBTCL_STDIN\fR,
\fBTCL_STDOUT\fR, and \fBTCL_STDERR\fR; if it is set, then it is an
error for argc and argv to override stdio channels for which
\fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, and \fBTCL_STDERR\fR have been set.
.PP
If an error occurs while opening the channel, \fBTcl_OpenCommandChannel\fR
returns NULL and records a POSIX error code that can be retrieved with
\fBTcl_GetErrno\fR.
In addition, \fBTcl_OpenCommandChannel\fR leaves an error message in
the interpreter's result if \fIinterp\fR is not NULL.
.PP
The newly created channel is not registered in the supplied interpreter; to
register it, use \fBTcl_RegisterChannel\fR, described below.
If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was
previously closed, the act of creating the new channel also assigns it as a
replacement for the standard channel.

.SH TCL_MAKEFILECHANNEL
.PP
\fBTcl_MakeFileChannel\fR makes a \fBTcl_Channel\fR from an existing,
platform-specific, file handle.
The newly created channel is not registered in the supplied interpreter; to
register it, use \fBTcl_RegisterChannel\fR, described below.
If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was
previously closed, the act of creating the new channel also assigns it as a
replacement for the standard channel.

.SH TCL_GETCHANNEL
.PP
\fBTcl_GetChannel\fR returns a channel given the \fIchannelName\fR used to
create it with \fBTcl_CreateChannel\fR and a pointer to a Tcl interpreter in
\fIinterp\fR. If a channel by that name is not registered in that interpreter,
the procedure returns NULL. If the \fImodePtr\fR argument is not NULL, it
points at an integer variable that will receive an OR-ed combination of
\fBTCL_READABLE\fR and \fBTCL_WRITABLE\fR describing whether the channel is
open for reading and writing.
.PP
\fBTcl_GetChannelNames\fR and \fBTcl_GetChannelNamesEx\fR write the
names of the registered channels to the interpreter's result as a
list object.  \fBTcl_GetChannelNamesEx\fR will filter these names
according to the \fIpattern\fR.  If \fIpattern\fR is NULL, then it
will not do any filtering.  The return value is \fBTCL_OK\fR if no
errors occurred writing to the result, otherwise it is \fBTCL_ERROR\fR,
and the error message is left in the interpreter's result.

.SH TCL_REGISTERCHANNEL
.PP
\fBTcl_RegisterChannel\fR adds a channel to the set of channels accessible
in \fIinterp\fR. 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 \fBTcl_CreateChannel\fR.  After this call,
the channel becomes the property of the interpreter, and the caller should
not call \fBTcl_Close\fR for the channel; the channel will be closed
automatically when it is unregistered from the interpreter.
.PP
Code executing outside of any Tcl interpreter can call
\fBTcl_RegisterChannel\fR with \fIinterp\fR 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 \fBTcl_UnregisterChannel\fR 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.
.PP
This procedure interacts with the code managing the standard
channels. If no standard channels were initialized before the first
call to \fBTcl_RegisterChannel\fR they will get initialized by that
call. See \fBTcl_StandardChannels\fR for a general treatise about
standard channels and the behaviour of the Tcl library with regard to
them.

.SH TCL_UNREGISTERCHANNEL
.PP
\fBTcl_UnregisterChannel\fR removes a channel from the set of channels
accessible in \fIinterp\fR. 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.
.PP
Code not associated with a Tcl interpreter can call
\fBTcl_UnregisterChannel\fR with \fIinterp\fR 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.  \fBTcl_UnregisterChannel\fR
is very similar to \fBTcl_DetachChannel\fR except that it will also
close the channel if no further references to it exist.

.SH TCL_DETACHCHANNEL
.PP
\fBTcl_DetachChannel\fR removes a channel from the set of channels
accessible in \fIinterp\fR. 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.
.PP
Code not associated with a Tcl interpreter can call
\fBTcl_DetachChannel\fR with \fIinterp\fR 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, unlike \fBTcl_UnregisterChannel\fR, 
it will not be closed.

.SH TCL_ISSTANDARDCHANNEL
.PP
\fBTcl_IsStandardChannel\fR tests whether a channel is one of the
three standard channels, stdin, stdout or stderr.  If so, it returns
1, otherwise 0.
.PP
No attempt is made to check whether the given channel or the standard 
channels are initialized or otherwise valid.

.SH TCL_CLOSE
.PP
\fBTcl_Close\fR destroys the channel \fIchannel\fR, which must denote a
currently open channel. The channel should not be registered in any
interpreter when \fBTcl_Close\fR 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.
.PP
If the channel was closed successfully, \fBTcl_Close\fR returns \fBTCL_OK\fR.
If an error occurs, \fBTcl_Close\fR returns \fBTCL_ERROR\fR and records a
POSIX error code that can be retrieved with \fBTcl_GetErrno\fR.
If the channel is being closed synchronously and an error occurs during
closing of the channel and \fIinterp\fR is not NULL, an error message is
left in the interpreter's result.
.PP
Note: it is not safe to call \fBTcl_Close\fR on a channel that has been
registered using \fBTcl_RegisterChannel\fR; see the documentation for
\fBTcl_RegisterChannel\fR, above, for details. If the channel has ever
been given as the \fBchan\fR argument in a call to
\fBTcl_RegisterChannel\fR, you should instead use
\fBTcl_UnregisterChannel\fR, which will internally call \fBTcl_Close\fR
when all calls to \fBTcl_RegisterChannel\fR have been matched by
corresponding calls to \fBTcl_UnregisterChannel\fR.

.VS 8.1 br
.SH "TCL_READCHARS AND TCL_READ"
.PP
\fBTcl_ReadChars\fR consumes bytes from \fIchannel\fR, converting the bytes
to UTF-8 based on the channel's encoding and storing the produced data in 
\fIreadObjPtr\fR's string representation.  The return value of
\fBTcl_ReadChars\fR is the number of characters, up to \fIcharsToRead\fR,
that were stored in \fIreadObjPtr\fR.  If an error occurs while reading, the
return value is \-1 and \fBTcl_ReadChars\fR records a POSIX error code that
can be retrieved with \fBTcl_GetErrno\fR.
.PP
The return value may be smaller than the value to read, indicating that less
data than requested was available.  This is called a \fIshort read\fR.  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:  \fBTcl_ReadChars\fR returns a short count rather than waiting
for more data.
.PP
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 \fBTcl_Eof\fR and \fBTcl_InputBlocked\fR to tell
which of these conditions actually occurred.
.PP
\fBTcl_ReadChars\fR translates the various end-of-line representations into
the canonical \fB\en\fR 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
\fBfconfigure\fR command.
.PP