Assert Parameter and Return

Assert Parameter and Return

An improved solution is an assertion macro that captures the logic “check parameter and return zero” in one place. Such a macro first tests a function parameter and if it fails, the macro will not only emit an assertion failure message, but will also tolerate the error by returning a specified default value from the function.

Here's a generic version for any condition:

    #define yassert_and_return(cond,retval) \
        if (cond) {} else { \
            aussie_yassert_fail(#cond " == NULL", __FILE__, __LINE__); \
            return (retval); \
        }

The usage of this function is:

    float aussie_vector_something(float v[], int n) 
    {
            yassert_and_return(v != NULL, 0.0f);
        ...
    }

The above version works for any condition. Here's another version specifically for testing an incoming function parameter for a NULL value:

    #define yassert_param_tolerate_null(var,retval) \
        if ((var) != NULL) {} else { \
            aussie_yassert_fail(#var " == NULL", __FILE__, __LINE__); \
            return (retval); \
        }

The usage of this function is:

    yassert_param_tolerate_null(v, 0.0f);

If you want to be picky, a slightly better version wraps the “if-else” logic inside a “do-while(0)” trick. This is a well-known trick to make a macro act more function-like in all statement structures.

    #define yassert_param_tolerate_null2(var,retval) \
        do { if ((var) != NULL) {} else { \
            aussie_yassert_fail(#var " == NULL", __FILE__, __LINE__); \
            return (retval); \
        }} while(0)

The idea of this macro is to avoid lots of parameter-checking boilerplate that will be laborious and error-prone. But it's also an odd style to hide a return statement inside a function-like preprocessor macro, so this is not a method that will suit everyone.

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