Tuesday, July 17, 2007

Debugging with Exception Breakpoints

How many times has this happened to you? You're working on code that's not quite functioning correctly. You suspect there's an exception being thrown somewhere, but it's being caught and ignored. Maybe this was intentional, or maybe it was poorly written code. Either way, you need to locate the problem. Visual Studio 2005 has a handy little tool to help - Exception Breakpoints.

Say you have code that looks like this:

int a = 2;
int b = 0;
int c = a / b; // does not compute
// Do nothing

If you were to run this code, you'd never know that there was a problem (well, not until you tried to use the value of 'c' elsewhere.) What we want to do is have the debugger break as soon as an exception is thrown. To do this, open the Exceptions dialog, either through the menu (Debug > Exceptions) or the keyboard shortcut (Ctrl+D followed by E).

Under the Thrown column, check the box next to the Common Language Runtime Exceptions. Now, when an exception is thrown, VS immediately breaks at the offending line of code. One word of warning - Depending on the size of the code, you may find far more exceptions being thrown than you had expected.

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