What is the use of "using namespace std"?

c++ namespaces std using
Jarvis picture Jarvis · Sep 20, 2013 · Viewed 248.7k times · Source

What is the use of using namespace std?

I'd like to see explanation in Layman terms.

Answer

Daniel Daranas picture Daniel Daranas · Sep 20, 2013
  • using: You are going to use it.
  • namespace: To use what? A namespace.
  • std: The std namespace (where features of the C++ Standard Library, such as string or vector, are declared).

After you write this instruction, if the compiler sees string it will know that you may be referring to std::string, and if it sees vector, it will know that you may be referring to std::vector. (Provided that you have included in your compilation unit the header files where they are defined, of course.)

If you don't write it, when the compiler sees string or vector it will not know what you are refering to. You will need to explicitly tell it std::string or std::vector, and if you don't, you will get a compile error.

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