What is the best way to return an error from a function when I'm already returning a value?

Question

I wrote a function in C that converts a string to an integer and returns the integer. When I call the function I also want it to let me know if the string is not a valid num

Answer 1

Well, the way that .NET handles this in Int32.TryParse is to return the success/failure, and pass the parsed value back with a pass-by-reference parameter. The same could be applied in C:

int intval(const char *string, s32 *parsed)
{
    *parsed = 0; // So that if we return an error, the value is well-defined

    // Normal code, returning error codes if necessary
    // ...

    *parsed = num;
    return SUCCESS; // Or whatever
}