Stroustrup's RAII and the cast operator FILE* () = contradiction?
c++, pointers, raii
Solution
Seems like it is inevitable evil price for comfort. Once you want a way `FILE*` be extractible from your fancy RAII class, it can be misused. Will it be `operator FILE*()` or `FILE* getRawPtr()` method, or whatever, it can be called on a temporarty object, making the result invalid just after it is returned.
In C++11, however, you can make this a little more secured, by disallowing this call on temporaries, like this:
operator FILE* () & { return p; }
// Note this -----^
Useful link on how it works provided by Morwenn in the comments: What is "rvalue reference for *this"?
Problem
I was reading through Stroustrup’s C++ (3ed, 1997) to see how he implemented the RAII, and on page 365 I found this: ``` class File_ptr{ FILE* p; public: File_ptr(const char* n, const char* a){p = fopen(n, a);} File_ptr(FILE* pp) { p = pp; } ~File_ptr() {fclose(p);} operator FILE* () {return p;} }; ``` The implementation of constructors and destructors is obvious and complies with the RAII idiom, but I don’t understand why he uses the `operator FILE* () {return p;}`. This would result in using `File_ptr` in the following way: ``` FILE* p = File_ptr("myfile.txt", "r"); ``` The result in a closed `p`, which is semantically inappropriate in this case. Also, if `File_ptr` is meant to be used as RAII, this operator allows it to be misused like in the example. Or am I missing something?