4 - Using ASSERTING()

• Use it validate function inputs and outputs - if a function is someday called with bad input, ASSERTING() will catch it.
• Use it to confirm invariants - items that shouldn't change in a section of code. Check both on entering a section and exiting.
• Use it to inject special time-consuming code. For instance, if you are coding a sort, you could create a routine to check the sort, and place the call in an ASSERTING(). Production code won't have the time-consuming check, while your debug version will.

Obviously, these are only a few ideas. Key to it all is that you are asserting a fact about the code, an assertion that the failure of which is going to cause you grief down the line. By checking everything immediately, you avoid that grief later on.

This column's program includes all of the necessary tool source, and is a simple tester, allowing you to trigger a variety of nifty errors and let you see the errors caught by the tools. For assertions, you can see what turning them off or breaking to the emulator is like. As well, there are a variety of errors generated for capture by our third and final tool.

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