Assertion Return Value Usage

Assertion Return Value Usage

Some programmers like to use an assertion style that tests the return code of their assert macro:

    if (assert(ptr != NULL)) {  // Risky
        // Normal code
        ptr->count++;
    }
    else {
        // Assertion failed
    }

This assertion style can be used if you like it, but I don't particularly recommend it, because it has a few risks:

1. The hidden assert failure function must return “false” so that “if” test fails when the assertion fails.

2. Embedding assertions deeply into the main code expressions increases the temptation to use side effects like “++” in the condition, which can quietly disappear if you ever remove the assertions from a production build:

    if (assert(++i >= 0))  // Risky

3. The usual assertion removal method of “((void)0)” will fail with compilation errors in an if statement. Also using a dummy replacement value of “0” is incorrect, and even “1” is not a great option, since the “if(assert(ptr!=NULL))” test becomes the unsafe “if(1)”. A safer removal method is a macro:

    #define assert(cond) (cond)

Or you can use an inline function:

    inline void assert(bool cond) { } // Empty

This avoids crashes, but may still leave debug code running (i.e. a slug, not a bug). It relies on the optimizer to remove any assertions that are not inside an “if” condition, which just leave a null-effect condition sitting there. Note also that this removal method with “(cond)” is also safer because keeping the condition also retains any side-effects in that condition (i.e. the optimizer won't remove those!).

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