C++ Library Conventions
The Standard C++ library obeys much the same conventions as the Standard C library, plus a few more outlined here.
Except for macro names, which obey no scoping rules, all names in the Standard C++ library are declared in the std
namespace. Including a Standard C++ header does not introduce any library names into the current
namespace. You must, for example, refer to the standard input stream cin as std::cin, even after including the header <iostream> that declares it. Alternatively, you can incorporate all members of the std
namespace into the current
namespace by writing:
using namespace std;
immediately after all include directives that name the standard headers. Note that the Standard C headers behave mostly as if they include no
namespace declarations. If you include, for example, <cstdlib>, you call std::abort() to cause abnormal termination, but if you include <stdlib.h>, you call abort().