Question

Can i safely use code like

fprintf(nullptr, "str");

or smth like

std::ofstream() << "str";

and

std::ofstream f;
f << "str";

Is there any descriptions of such situations in the C / C++ Standards?

Answer 1

When using C++ streams the output operations have no effect when they are sent to stream with std::ios_base::failbit or std::ios_base::badbit set. If it is acceptable that the stream doesn’t indicate success, you can just create an std::ostream with a null stream buffer:

std::ostream nullstream(0);

If you want the stream to also indicate success, you can just use it with a stream buffer indicating success from overflow() and sync() but not doing anything.