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author | William Joye <wjoye@cfa.harvard.edu> | 2016-12-21 22:56:22 (GMT) |
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committer | William Joye <wjoye@cfa.harvard.edu> | 2016-12-21 22:56:22 (GMT) |
commit | d1a6de55efc90f190dee42ab8c4fa9070834e77d (patch) | |
tree | ec633f5608ef498bee52a5f42c12c49493ec8bf8 /tcl8.6/doc/GetStdChan.3 | |
parent | 5514e37335c012cc70f5b9aee3cedfe3d57f583f (diff) | |
parent | 98acd3f494b28ddd8c345a2bb9311e41e2d56ddd (diff) | |
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Merge commit '98acd3f494b28ddd8c345a2bb9311e41e2d56ddd' as 'tcl8.6'
Diffstat (limited to 'tcl8.6/doc/GetStdChan.3')
-rw-r--r-- | tcl8.6/doc/GetStdChan.3 | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/tcl8.6/doc/GetStdChan.3 b/tcl8.6/doc/GetStdChan.3 new file mode 100644 index 0000000..be0e79f --- /dev/null +++ b/tcl8.6/doc/GetStdChan.3 @@ -0,0 +1,86 @@ +'\" +'\" Copyright (c) 1996 by Sun Microsystems, Inc. +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +.TH Tcl_GetStdChannel 3 7.5 Tcl "Tcl Library Procedures" +.so man.macros +.BS +'\" Note: do not modify the .SH NAME line immediately below! +.SH NAME +Tcl_GetStdChannel, Tcl_SetStdChannel \- procedures for retrieving and replacing the standard channels +.SH SYNOPSIS +.nf +\fB#include <tcl.h>\fR +.sp +Tcl_Channel +\fBTcl_GetStdChannel\fR(\fItype\fR) +.sp +\fBTcl_SetStdChannel\fR(\fIchannel, type\fR) +.sp +.SH ARGUMENTS +.AS Tcl_Channel channel +.AP int type in +The identifier for the standard channel to retrieve or modify. Must be one of +\fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, or \fBTCL_STDERR\fR. +.AP Tcl_Channel channel in +The channel to use as the new value for the specified standard channel. +.BE + +.SH DESCRIPTION +.PP +Tcl defines three special channels that are used by various I/O related +commands if no other channels are specified. The standard input channel +has a channel name of \fBstdin\fR and is used by \fBread\fR and \fBgets\fR. +The standard output channel is named \fBstdout\fR and is used by +\fBputs\fR. The standard error channel is named \fBstderr\fR and is used for +reporting errors. In addition, the standard channels are inherited by any +child processes created using \fBexec\fR or \fBopen\fR in the absence of any +other redirections. +.PP +The standard channels are actually aliases for other normal channels. The +current channel associated with a standard channel can be retrieved by calling +\fBTcl_GetStdChannel\fR with one of +\fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, or \fBTCL_STDERR\fR as the \fItype\fR. The +return value will be a valid channel, or NULL. +.PP +A new channel can be set for the standard channel specified by \fItype\fR +by calling \fBTcl_SetStdChannel\fR with a new channel or NULL in the +\fIchannel\fR argument. If the specified channel is closed by a later call to +\fBTcl_Close\fR, then the corresponding standard channel will automatically be +set to NULL. +.PP +If a non-NULL value for \fIchannel\fR is passed to \fBTcl_SetStdChannel\fR, +then that same value should be passed to \fBTcl_RegisterChannel\fR, like so: +.PP +.CS +Tcl_RegisterChannel(NULL, channel); +.CE +.PP +This is a workaround for a misfeature in \fBTcl_SetStdChannel\fR that it +fails to do some reference counting housekeeping. This misfeature cannot +be corrected without contradicting the assumptions of some existing +code that calls \fBTcl_SetStdChannel\fR. +.PP +If \fBTcl_GetStdChannel\fR is called before \fBTcl_SetStdChannel\fR, Tcl will +construct a new channel to wrap the appropriate platform-specific standard +file handle. If \fBTcl_SetStdChannel\fR is called before +\fBTcl_GetStdChannel\fR, then the default channel will not be created. +.PP +If one of the standard channels is set to NULL, either by calling +\fBTcl_SetStdChannel\fR with a NULL \fIchannel\fR argument, or by calling +\fBTcl_Close\fR on the channel, then the next call to \fBTcl_CreateChannel\fR +will automatically set the standard channel with the newly created channel. If +more than one standard channel is NULL, then the standard channels will be +assigned starting with standard input, followed by standard output, with +standard error being last. +.PP +See \fBTcl_StandardChannels\fR for a general treatise about standard +channels and the behavior of the Tcl library with regard to them. + +.SH "SEE ALSO" +Tcl_Close(3), Tcl_CreateChannel(3), Tcl_Main(3), tclsh(1) + +.SH KEYWORDS +standard channel, standard input, standard output, standard error |