Why isn't 'nullptr' in the 'std' namespace?

问题

It seems that nullptr is declared in the default global namespace. Wouldn't it make sense for it to be in the std namespace?

回答1:

nullptr is a C++11 keyword (no different to if, public, true, void, etc.), so namespaces don't apply.

回答2:

nullptr is a pointer literal the same way as for example true is a boolean literal. This literal has type std::nullptr_t that is as you see this type is defined in name space std:: The pointer literal is described in section 2.14.7 Pointer literals of the C++ Standard.

来源：https://stackoverflow.com/questions/21510121/why-isnt-nullptr-in-the-std-namespace