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Diffstat (limited to 'doc/catch.n')
| -rw-r--r-- | doc/catch.n | 117 |
1 files changed, 81 insertions, 36 deletions
diff --git a/doc/catch.n b/doc/catch.n index 01770aa..94fa5dd 100644 --- a/doc/catch.n +++ b/doc/catch.n @@ -1,27 +1,25 @@ '\" '\" Copyright (c) 1993-1994 The Regents of the University of California. '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. +'\" Contributions from Don Porter, NIST, 2003. (not subject to US copyright) '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: catch.n,v 1.5.18.2 2004/11/09 10:25:23 dkf Exp $ -'\" +.TH catch n "8.5" Tcl "Tcl Built-In Commands" .so man.macros -.TH catch n "8.0" Tcl "Tcl Built-In Commands" .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME catch \- Evaluate script and trap exceptional returns .SH SYNOPSIS -\fBcatch\fI script \fR?\fIvarName\fR? +\fBcatch\fI script \fR?\fIresultVarName\fR? ?\fIoptionsVarName\fR? .BE - .SH DESCRIPTION .PP The \fBcatch\fR command may be used to prevent errors from aborting command -interpretation. The \fBcatch\fR command calls the Tcl interpreter recursively to -execute \fIscript\fR, and always returns without raising an error, +interpretation. The \fBcatch\fR command calls the Tcl interpreter recursively +to execute \fIscript\fR, and always returns without raising an error, regardless of any errors that might occur while executing \fIscript\fR. .PP If \fIscript\fR raises an error, \fBcatch\fR will return a non-zero integer @@ -34,47 +32,94 @@ by a return code of \fBTCL_ERROR\fR. The other exceptional return codes are returned by the \fBreturn\fR, \fBbreak\fR, and \fBcontinue\fR commands and in other special situations as documented. Tcl packages can define new commands that return other integer values as return codes as well, -and scripts that make use of the \fBreturn -code\fR command can also +and scripts that make use of the \fBreturn \-code\fR command can also have return codes other than the five defined by Tcl. .PP -If the \fIvarName\fR argument is given, then the variable it names is -set to the result of the script evaluation. When the return code from -the script is 1 (\fBTCL_ERROR\fR), the value stored in \fIvarName\fR is an error -message. When the return code from the script is 0 (\fBTCL_OK\fR), the value -stored in \fIresultVarName\fR is the value returned from \fIscript\fR. +If the \fIresultVarName\fR argument is given, then the variable it names is +set to the result of the script evaluation. When the return code from the +script is 1 (\fBTCL_ERROR\fR), the value stored in \fIresultVarName\fR is an +error message. When the return code from the script is 0 (\fBTCL_OK\fR), the +value stored in \fIresultVarName\fR is the value returned from \fIscript\fR. +.PP +If the \fIoptionsVarName\fR argument is given, then the variable it +names is set to a dictionary of return options returned by evaluation +of \fIscript\fR. Tcl specifies two entries that are always +defined in the dictionary: \fB\-code\fR and \fB\-level\fR. When +the return code from evaluation of \fIscript\fR is not \fBTCL_RETURN\fR, +the value of the \fB\-level\fR entry will be 0, and the value +of the \fB\-code\fR entry will be the same as the return code. +Only when the return code is \fBTCL_RETURN\fR will the values of +the \fB\-level\fR and \fB\-code\fR entries be something else, as +further described in the documentation for the \fBreturn\fR command. .PP -If \fIscript\fR does not raise an error, \fBcatch\fR will return 0 -(\fBTCL_OK\fR) and set the variable to the value returned from \fIscript\fR. +When the return code from evaluation of \fIscript\fR is +\fBTCL_ERROR\fR, four additional entries are defined in the dictionary +of return options stored in \fIoptionsVarName\fR: \fB\-errorinfo\fR, +\fB\-errorcode\fR, \fB\-errorline\fR, and +.VS 8.6 +\fB\-errorstack\fR. +.VE 8.6 +The value of the \fB\-errorinfo\fR entry is a formatted stack trace containing +more information about the context in which the error happened. The formatted +stack trace is meant to be read by a person. The value of the +\fB\-errorcode\fR entry is additional information about the error stored as a +list. The \fB\-errorcode\fR value is meant to be further processed by +programs, and may not be particularly readable by people. The value of the +\fB\-errorline\fR entry is an integer indicating which line of \fIscript\fR +was being evaluated when the error occurred. +.VS 8.6 +The value of the \fB\-errorstack\fR entry is an +even-sized list made of token-parameter pairs accumulated while +unwinding the stack. The token may be +.QW \fBCALL\fR , +in which case the parameter is a list made of the proc name and arguments at +the corresponding level; or it may be +.QW \fBUP\fR , +in which case the parameter is +the relative level (as in \fBuplevel\fR) of the previous \fBCALL\fR. The +salient differences with respect to \fB\-errorinfo\fR are that: +.IP [1] +it is a machine-readable form that is amenable to processing with +[\fBforeach\fR {tok prm} ...], +.IP [2] +it contains the true (substituted) values passed to the functions, instead of +the static text of the calling sites, and +.IP [3] +it is coarser-grained, with only one element per stack frame (like procs; no +separate elements for \fBforeach\fR constructs for example). +.VE 8.6 .PP -Note that \fBcatch\fR catches all exceptions, including those -generated by \fBbreak\fR and \fBcontinue\fR as well as errors. The -only errors that are not caught are syntax errors found when the -script is compiled. This is because the catch command only catches -errors during runtime. When the catch statement is compiled, the -script is compiled as well and any syntax errors will generate a Tcl -error. - +The values of the \fB\-errorinfo\fR and \fB\-errorcode\fR entries of +the most recent error are also available as values of the global +variables \fB::errorInfo\fR and \fB::errorCode\fR respectively. +.VS 8.6 +The value of the \fB\-errorstack\fR entry surfaces as \fBinfo errorstack\fR. +.VE 8.6 +.PP +Tcl packages may provide commands that set other entries in the +dictionary of return options, and the \fBreturn\fR command may be +used by scripts to set return options in addition to those defined +above. .SH EXAMPLES +.PP The \fBcatch\fR command may be used in an \fBif\fR to branch based on the success of a script. +.PP .CS if { [\fBcatch\fR {open $someFile w} fid] } { - puts stderr "Could not open $someFile for writing\\n$fid" + puts stderr "Could not open $someFile for writing\en$fid" exit 1 } .CE .PP -The \fBcatch\fR command will not catch compiled syntax errors. The -first time proc \fBfoo\fR is called, the body will be compiled and a -Tcl error will be generated. -.CS -proc foo {} { - \fBcatch\fR {expr {1 +- }} -} -.CE - +There are more complex examples of \fBcatch\fR usage in the +documentation for the \fBreturn\fR command. .SH "SEE ALSO" -break(n), continue(n), error(n), return(n), tclvars(n) - +break(n), continue(n), dict(n), error(n), errorCode(n), errorInfo(n), info(n), +return(n) .SH KEYWORDS -catch, error +catch, error, exception +'\" Local Variables: +'\" mode: nroff +'\" fill-column: 78 +'\" End: |