Namespace aliases

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

C++ language

 

Declarations

Overview declaration syntax decl-specifier-seq declarator Specifiers typedef inline function specifier virtual function specifier explicit function specifier friend constexpr (C++11) storage class specifiers class union enum decltype (C++11) auto (C++11) alignas (C++11) const/volatile elaborated type specifier attributes (C++11) Declarators reference pointer array

Block declarations simple-declaration alias declaration(C++11) namespace alias definition using-declaration using-directive static_assert declaration (C++11) asm-definition opaque enum declaration(C++11) Other declarations namespace definition function declaration class template declaration function template declaration explicit template instantiation(C++11) explicit template specialization linkage specification attribute declaration (C++11) empty declaration

 

Namespace aliases allow the programmer to define an alternate name for a namespace.

They are commonly used as a convenient shortcut for long or deeply-nested namespaces.

Syntax

namespace alias_name = ns_name;	(1)
namespace alias_name = ::ns_name;	(2)
namespace alias_name = nested_name::ns_name;	(3)

Explanation

The new alias alias_name provides an alternate method of accessing ns_name.

alias_name must be a name not previously used. alias_name is valid for the duration of the scope in which it is introduced.

Example

Run this code

#include <iostream>
 
namespace foo {
    namespace bar {
         namespace baz {
             int qux = 42;
         }
    }
}
 
namespace fbz = foo::bar::baz;
 
int main()
{
    std::cout << fbz::qux << '\n';
}

Output:

42

See also

namespace declaration

identifies a namespace