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Exceptions - Tcl style
Checking for all possible errors isn't a "failsafe" way of coding. If you try and check for absolutely any error, you're still very likely to miss one or two possibilities, and it's fare better to add a block to your code to say (in essence) "if anything at all goes wrong, go here...". And that's commonly known as throwing and catching exceptions. Tcl has a catch command: catch {code block} varnamein which you can wrap a piece of code from which you want to catch exceptions. The result of running the block - either its return value or error message - will be saved into the named variable. Catch also return a true / false boolean so that you know whether or not an exception was thrown. So - put your catch into an if block ... and add exception handling code in the optional block. There's a full example [here] from the Tcl course I was teaching yesterday. Tcl also supports an unknown command, which is run if you ask for a command that's not defined to be run. That's a further type of exception catching - also illustrated in the example that I've linked to above. (written 2011-05-12) Associated topics are indexed under T214 - Tcl/Tk - Other Facilities in Tcl[3583] Expanding a list of parameters in Tcl - {*} and eval - (2012-01-17) [3570] Trapping errors in Tcl - the safety net that catch provides - (2012-01-06) [2467] Tcl - catching an error before your program crashes - (2009-10-22) [1338] Handling Binary data in Tcl (with a note on C) - (2007-09-09) [1334] Stable sorting - Tcl, Perl and others - (2007-09-06) [1277] AgtInvoke - a command to drive Agilent Tcl software extensions - (2007-07-26) [782] Converting between Hex and Decimal in Tcl - (2006-06-28) [748] Getting rid of variables after you have finished with them - (2006-06-06) [461] Shortened interactive commands - (2005-10-11) [366] Error handling in Tcl through catch - (2005-07-02) [364] pu daily and p hourly - (2005-06-30) [239] What and why for the epoch - (2005-03-08)
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