Error generation and handling

TWAPI error generation and handling


map_windows_error ERRORCODE
win32_error WINERROR ?MESSAGE?


This module provides various facilities for generating and handing errors and Tcl exceptions.

Error generation

TWAPI generates Tcl exceptions when errors are encountered. Information pertaining to the error is stored in Tcl global variables as with any standard Tcl errors. The global variable errorInfo contains a traceback of the Tcl stack when the error occured. The global errorCode contains a list with additional information about the error. The first element is the error class and determines the format of the rest of the list. This may take one of the following values:

TWAPI_WIN32 This error class corresponds to Windows error codes. The second element of the list is the integer Windows error code. The third element is the corresponding localized text string describing the error. The fourth element is optional and its format is dependent on the specific error code.

The command win32_error can be used to generate an error in this format.
TWAPI This error class is used for non-Windows related errors, for example invalid options to commands. The format is similar to that of TWAPI_WIN32 except that the error code is an internal TWAPI error code and the text is not localized.

Error handling

Several TWAPI commands pertain to error handling. map_windows_error returns the text description of an operating system error code.

try provides exception handling with finalization features.


map_windows_error ERRORCODE
Returns the text string corresponding to a Windows error code.
The command executes SCRIPT in the caller's context. If the script completes without generating any Tcl exceptions, the command executes the script FINALSCRIPT if specified. The result of the command is the result of SCRIPT.

If SCRIPT generates any errors, the command matches the Tcl global ::errorCode variable against each specified ERRORPATTERN in turn. When the first match is found, the corresponding ERRORSCRIPT is executed. Then FINALSCRIPT is executed if specified. The return value from the command is the result of the executed ERRORSCRIPT script.

If the none of the ERRORPATTERN arguments match when an error occurs in SCRIPT, the command executes FINALSCRIPT if specified, and then regenerates the original error.

Each ERRORPATTERN should be a list and is matched against the first (facility) and second (code) elements of ::errorCode. If ERRORPATTERN is empty, it matches any value of ::errorCode. If ERRORPATTERN contains only one element, it is matched against the first element of ::errorCode with the second field of ::errorCode not used for matching. When matching against the second element of ::errorCode, first a exact string match is tried and if that fails, an integer match is tried if both operands being compared are valid integers.

When a ERRORSCRIPT script is run, the global Tcl variables ::errorCode, ::errorInfo are automatically brought into scope without needing a global statement in the script and contain the values set when SCRIPT generated the error. In addition, the variable ::errorResult is set to the error message set by the original error. This behavior is similar to the try_eval command from TclX.
win32_error WINERROR ?MESSAGE?
Generates a Tcl exception corresponding to the Windows error code WINERROR. MESSAGE may be specified as the error message in which case the system error message for WINERROR is appended to it.


Copyright © 2003-2009 Ashok P. Nadkarni

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