Editing Namespace (section)

=====C++=====
In [[C++]], a namespace is defined with a namespace block.<ref>{{cite web|url=http://www.cplusplus.com/doc/tutorial/namespaces/ |title=Namespaces allow to group entities like classes, objects and functions under a name. |publisher=Cplusplus.com |access-date=2011-07-26}}</ref>
<syntaxhighlight lang="cpp">
namespace abc {
    int bar;
}
</syntaxhighlight>
Within this block, identifiers can be used exactly as they are declared. Outside of this block, the namespace specifier must be prefixed. For example, outside of <code>namespace abc</code>, <code>bar</code> must be written <code>abc::bar</code> to be accessed. C++ includes another construct that makes this verbosity unnecessary. By adding the line
<syntaxhighlight lang="cpp">
using namespace abc;
</syntaxhighlight>
to a piece of code, the prefix <code>abc::</code> is no longer needed.

Identifiers that are not explicitly declared within a namespace are considered to be in the global namespace.
<syntaxhighlight lang="cpp">
int foo;
</syntaxhighlight>
These identifiers can be used exactly as they are declared, or, since the global namespace is unnamed, the namespace specifier <code>::</code> can be prefixed. For example, <code>foo</code> can also be written <code>::foo</code>.

Namespace resolution in C++ is hierarchical. This means that within the hypothetical namespace <code>food::soup</code>, the identifier <code>chicken</code> refers to <code>food::soup::chicken</code>. If <code>food::soup::chicken</code> doesn't exist, it then refers to <code>food::chicken</code>. If neither <code>food::soup::chicken</code> nor <code>food::chicken</code> exist, <code>chicken</code> refers to <code>::chicken</code>, an identifier in the global namespace.

Namespaces in C++ are most often used to avoid [[naming collision]]s. Although namespaces are used extensively in recent C++ code, most older code does not use this facility because it did not exist in early versions of the language. For example, the entire [[C++ Standard Library]] is defined within <code>namespace std</code>, but before standardization many components were originally in the global namespace. A programmer can insert the <code>using</code> directive to bypass namespace resolution requirements and obtain backwards compatibility with older code that expects all identifiers to be in the global namespace. However the use of the <code>using</code> directive for reasons other than backwards compatibility (e.g., convenience) is considered to be against good code practices.