Question

My String class provides an operator char* overload to allow you to pass the string to C functions.

Unfortunately a colleague of mine just inadvertently discovered a bug.

He effectively had the following code.

StringT str;
// Some code.
delete str;

Is there anyway to prevent delete from casting the string object to a char* to prevent future bugs like this cropping up? std::string gets round this problem by not providing a char operator overload but, ideally, I’d like to keep the overload but prevent that delete from working.

Answer 1

Yes. Provide TWO implicit casts, by declaring (but not defining!) operator char const volatile*. When you’re passing your StringT to a C string function, overload resolution will still select your original operator char const* (exact match). But delete str; now becomes ambiguous.

The declaration can be private, so if it would somehow be selected will be a compile-time error. The intended ambiguity occurs before overload resolution – the private only serves to catch the exceedingly rare cases where the volatile overload would be selected somehow.