Initialize All Variables at Their Points of Declaration

I was reading a book recently called Code Craft - The Practice of Writing Excellent Code and one of the comments struck a particular chord with me as it brought back memories of an upgrade that went horribly wrong.  At least for me.

There was a brief section called "Initialize All Variables at Their Points of Declaration".  Now, this may seem self explanatory and quite normal to some people, but others think that this is rather strange.  "Why would I initialize a variable that I may never use?"  The problem is, that not everyone follows the same coding practices in real life.  Sometimes the compilers help/hurt us in this regard.  Back when I was predominantly working on the mainframe, we were switching from an older version of COBOL to COBOL II.  Ooh.  COBOL.  I can see your eyes glazing over.  Stay with me, there is method to my madness.

The process of conversion was really quite simple.  Recompile.  It wasn't that hard.  However, we discovered a little bit of a problem.  When we did our testing we discovered that we were occasionally getting OC7 (data exception) errors when everything should have been working.  Indeed, running the program multiple times against the same data actually generated different results.  After a lot of head scratching we determined that the problem lay in the fact that the old compiler, by default, initialized variables when they were defined.  COBOL II did not do this by default.  When the application was loaded into memory it would occasionally access memory that had been initialized for some other purpose and the program would work.  Other times, however, it was accessing "garbage" and the program would blow up.  If the original developer had initialized the variables in the fist place we never would have had a problem.

So, we made a small change and everything was perfect.

Almost.  Because of how we were doing the upgrade process I had to baby sit the recompilation of 1900 COBOL programs in 4 different environments (7600 recompiles altogether).  Took almost 48 hours to do it and I got almost no sleep, and all because someone failed to initialize a couple of variables.