development gotcha: incorrect data types

The other day I ran into a code bug that took a while to figure out.  It was so unique (to me) that I thought I’d write about it.

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The following pseudo code contains the bug.  The symptom was that mid-execution, the value of position was getting corrupted and thus causing a GPF 1 at the sprintf.

Did you spot the bug?!

I had mistakenly declared timerInterval as an int, rather than a double.  And because I’m not in the habit of error-checking the CVI standard library, the call to GetAsyncTimerAttribute blindly overfilled timerInterval with its double value, which then overwrote the value of position.

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position was the collateral damage because it’s declared before timerInterval.

Now curiously, when I tried to reproduce this bug on another machine, position retained its 0 initialized value.  So you can see how insidious this kind of bug can be — you might not even see it on all machines or at every runtime call.


  1. General Protection Fault

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