Namespace aliases

 

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Overview declaration syntax decl-specifier-seq declarator Specifiers typedef inline virtual function specifier explicit function specifier    friend constexpr (C++11) consteval (C++20) constinit (C++20) storage class specifiers translation-unit-local (C++20) class/struct union enum decltype (C++11) auto (C++11) alignas (C++11) constvolatile elaborated type specifier attributes (C++11)

Declarators reference pointer array Block declarations simple-declaration → structured binding declaration (C++17) alias declaration(C++11) namespace alias definition using-declaration using-directive static_assert declaration (C++11) asm-declaration 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
type alias declaration (C++11)	creates a synonym for a type