| 1 | '\" |
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| 2 | '\" Copyright (c) 1993 The Regents of the University of California. |
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| 3 | '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. |
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| 4 | '\" |
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| 5 | '\" See the file "license.terms" for information on usage and redistribution |
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| 6 | '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
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| 7 | '\" |
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| 8 | '\" RCS: @(#) $Id: error.n,v 1.11 2007/12/13 15:22:32 dgp Exp $ |
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| 9 | '\" |
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| 10 | .so man.macros |
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| 11 | .TH error n "" Tcl "Tcl Built-In Commands" |
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| 12 | .BS |
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| 13 | '\" Note: do not modify the .SH NAME line immediately below! |
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| 14 | .SH NAME |
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| 15 | error \- Generate an error |
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| 16 | .SH SYNOPSIS |
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| 17 | \fBerror \fImessage\fR ?\fIinfo\fR? ?\fIcode\fR? |
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| 18 | .BE |
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| 19 | |
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| 20 | .SH DESCRIPTION |
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| 21 | .PP |
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| 22 | Returns a \fBTCL_ERROR\fR code, which causes command interpretation to be |
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| 23 | unwound. \fIMessage\fR is a string that is returned to the application |
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| 24 | to indicate what went wrong. |
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| 25 | .PP |
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| 26 | The \fB\-errorinfo\fR return option of an interpreter is used |
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| 27 | to accumulate a stack trace of what was in progress when an |
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| 28 | error occurred; as nested commands unwind, |
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| 29 | the Tcl interpreter adds information to the \fB\-errorinfo\fR |
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| 30 | return option. If the \fIinfo\fR argument is present, it is |
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| 31 | used to initialize the \fB\-errorinfo\fR return options and |
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| 32 | the first increment of unwind information |
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| 33 | will not be added by the Tcl interpreter. |
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| 34 | In other |
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| 35 | words, the command containing the \fBerror\fR command will not appear |
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| 36 | in the stack trace; in its place will be \fIinfo\fR. |
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| 37 | Historically, this feature had been most useful in conjunction |
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| 38 | with the \fBcatch\fR command: |
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| 39 | if a caught error cannot be handled successfully, \fIinfo\fR can be used |
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| 40 | to return a stack trace reflecting the original point of occurrence |
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| 41 | of the error: |
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| 42 | .CS |
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| 43 | \fBcatch {...} errMsg |
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| 44 | set savedInfo $::errorInfo |
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| 45 | \&... |
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| 46 | error $errMsg $savedInfo\fR |
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| 47 | .CE |
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| 48 | When working with Tcl 8.5 or later, the following code |
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| 49 | should be used instead: |
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| 50 | .CS |
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| 51 | \fBcatch {...} errMsg options |
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| 52 | \&... |
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| 53 | return -options $options $errMsg\fR |
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| 54 | .CE |
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| 55 | .PP |
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| 56 | If the \fIcode\fR argument is present, then its value is stored |
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| 57 | in the \fB\-errorcode\fR return option. The \fB\-errorcode\fR |
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| 58 | return option is intended to hold a machine-readable description |
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| 59 | of the error in cases where such information is available; see |
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| 60 | the \fBreturn\fR manual page for information on the proper format |
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| 61 | for this option's value. |
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| 62 | .SH EXAMPLE |
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| 63 | Generate an error if a basic mathematical operation fails: |
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| 64 | .CS |
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| 65 | if {1+2 != 3} { |
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| 66 | \fBerror\fR "something is very wrong with addition" |
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| 67 | } |
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| 68 | .CE |
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| 69 | |
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| 70 | .SH "SEE ALSO" |
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| 71 | catch(n), return(n) |
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| 72 | |
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| 73 | .SH KEYWORDS |
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| 74 | error |
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