No you can't. "null" isn't a specific thing in c++. There's nullptr, NULL, and 0. NULL is just a fancy name for 0. If for example you have a function with a re

No you can't. "null" isn't a specific thing in c++. There's nullptr, NULL, and 0. NULL is just a fancy name for 0. If for example you have a function with a return type of string, it must return a string. It cannot return nullptr, NULL, or 0. It could return an empty string. But in some cases you might want to distinguish between empty string and no result, in that case you would want to the return type to be std::optional<std::string> .