Two-Minute Lecture on ErrorMode Function No-Nos

Keywords:   errormode(@off) errormode(@cancel)

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Read ALL the stuff about errormode in the manual. Only disable Errormode for one line at a time. Turning Errormode(@off) is a very big no-no almost all the time.

1. Use of Errormode indiscriminately will turn a 5 minute debugging project into a 6 week project.

2. ONLY put error mode around SINGLE statements where you are handling the errors yourself. If it is obvious that there is no way a statement could fail it should be run with ErrorMode(@CANCEL)

3. The problem is that the most mindless errors that you do not bother to check for will be the ones that set up a condition that causes a catastrophe 20 statements later.

4. Here's the famous case:

   User writes a script that deletes all the temp files from his temp directory at startup. Sometimes there are no files so errors were suppressed to avoid messages. Script read:

           ErrorMode(@OFF)
           DirChange("C:\TEMP")
           FileDelete("*.*")
   

   and he put the script in his startup directory. Everything ran fine for months.

   Then, being short of disk space on C:, moved the temp directory to D:\TEMP

   Next time boot up occurred, the script was run. The DirChange failed but because error mode was @OFF, the script continued to run.

   Needless to mention, the FileDelete("*.*") performed flawlessly. Too bad it was not pointing to any intended directory.

5. Use of ErrorMode(@OFF) at the top of your script WILL nail you every time. Basically your Faustian bargains are:
   • Your script will sometimes put an error message up in front of the user for untrapped errors. Your programming abilities will be held up to ridicule.

   • Your script will occasionally trash a computer requiring reformatting the hard drive and re-installing windows, losing all the users files in the process. This will be pointed out to your management. The humor of the situation will not be a migitating factor.

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Article ID:   W12710

Filename:   Two Minute Lecture on ErrorMode No-Nos.txt