GNU Compiler Collection (GCC) Internals: Namespaces

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#### 11.10.2 Namespaces

The root of the entire intermediate representation is the variable `global_namespace`. This is the namespace specified with `::` in C++ source code. All other namespaces, types, variables, functions, and so forth can be found starting with this namespace.

However, except for the fact that it is distinguished as the root of the representation, the global namespace is no different from any other namespace. Thus, in what follows, we describe namespaces generally, rather than the global namespace in particular.

A namespace is represented by a `NAMESPACE_DECL` node.

The following macros and functions can be used on a `NAMESPACE_DECL`:

`DECL_NAME`

  This macro is used to obtain the `IDENTIFIER_NODE` corresponding to the unqualified name of the name of the namespace (see Identifiers). The name of the global namespace is ‘`::`’, even though in C++ the global namespace is unnamed. However, you should use comparison with `global_namespace`, rather than `DECL_NAME` to determine whether or not a namespace is the global one. An unnamed namespace will have a `DECL_NAME` equal to `anonymous_namespace_name`. Within a single translation unit, all unnamed namespaces will have the same name.

`DECL_CONTEXT`

  This macro returns the enclosing namespace. The `DECL_CONTEXT` for the `global_namespace` is `NULL_TREE`.

`DECL_NAMESPACE_ALIAS`

  If this declaration is for a namespace alias, then `DECL_NAMESPACE_ALIAS` is the namespace for which this one is an alias.

  Do not attempt to use `cp_namespace_decls` for a namespace which is an alias. Instead, follow `DECL_NAMESPACE_ALIAS` links until you reach an ordinary, non-alias, namespace, and call `cp_namespace_decls` there.

`DECL_NAMESPACE_STD_P`

  This predicate holds if the namespace is the special `::std` namespace.

`cp_namespace_decls`

  This function will return the declarations contained in the namespace, including types, overloaded functions, other namespaces, and so forth. If there are no declarations, this function will return `NULL_TREE`. The declarations are connected through their `TREE_CHAIN` fields.

  Although most entries on this list will be declarations, `TREE_LIST` nodes may also appear. In this case, the `TREE_VALUE` will be an `OVERLOAD`. The value of the `TREE_PURPOSE` is unspecified; back ends should ignore this value. As with the other kinds of declarations returned by `cp_namespace_decls`, the `TREE_CHAIN` will point to the next declaration in this list.

  For more information on the kinds of declarations that can occur on this list, See Declarations. Some declarations will not appear on this list. In particular, no `FIELD_DECL`, `LABEL_DECL`, or `PARM_DECL` nodes will appear here.

  This function cannot be used with namespaces that have `DECL_NAMESPACE_ALIAS` set.

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