So it's actually printing *(const char **)&s?

The first pointer-sized chunk of the string structure is a pointer to the C-string representation. So the cast works as written.

Well, no, because (const char *)str is nonsense, if str is an std::string.

Not to the debugger. If the first 8 bytes of the object referenced by str is a char* the debugger is perfectly capable of using it that way.