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Namespace aliases - cppreference.com

From cppreference.com

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)
namespace alias_name = splice-specifier; (4) (since C++26)
alias_name - an identifier
ns_name - a (possibly qualified) identifier that names a namespace or namespace alias
splice-specifier - a splice specifier that designates a namespace that is not the global namespace

Explanation

The new alias alias_name provides an alternate method of accessing ns_name or the namespace designated by splice-specifier(since C++26).

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

Keywords

namespace

Example

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

Output:

See also