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C++ and C libraries and the std namespace

All C++ standard library names, including the C library names, if you include them, are defined in the namespace std.

Standard library names are defined using the following C++ syntax:

#include <cstdlib> // instead of stdlib.h

This means that you must qualify all the library names using one of the following methods:

  • Specify the standard namespace, for example:

  • Use the C++ keyword using to import a name to the global namespace:

    using namespace std;


errno is a macro, so it is not necessary to qualify it with a namespace.