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This section covers the various kinds of declarations that appear in the internal representation, except for declarations of functions (represented by FUNCTION_DECL nodes), which are described in Functions.

Some macros can be used with any kind of declaration. These include:

This macro returns an IDENTIFIER_NODE giving the name of the entity.
This macro returns the type of the entity declared.
This macro returns the name of the file in which the entity was declared, as a char*. For an entity declared implicitly by the compiler (like __builtin_memcpy), this will be the string "<internal>".
This macro returns the line number at which the entity was declared, as an int.
This predicate holds if the declaration was implicitly generated by the compiler. For example, this predicate will hold of an implicitly declared member function, or of the TYPE_DECL implicitly generated for a class type. Recall that in C++ code like:
          struct S {};

is roughly equivalent to C code like:

          struct S {};
          typedef struct S S;
The implicitly generated typedef declaration is represented by a TYPE_DECL for which DECL_ARTIFICIAL holds.
This predicate holds if the entity was declared at a namespace scope.
This predicate holds if the entity was declared at a class scope.
This predicate holds if the entity was declared inside a function body.

The various kinds of declarations include:

These nodes are used to represent labels in function bodies. For more information, see Functions. These nodes only appear in block scopes.
These nodes are used to represent enumeration constants. The value of the constant is given by DECL_INITIAL which will be an INTEGER_CST with the same type as the TREE_TYPE of the CONST_DECL, i.e., an ENUMERAL_TYPE.
These nodes represent the value returned by a function. When a value is assigned to a RESULT_DECL, that indicates that the value should be returned, via bitwise copy, by the function. You can use DECL_SIZE and DECL_ALIGN on a RESULT_DECL, just as with a VAR_DECL.
These nodes represent typedef declarations. The TREE_TYPE is the type declared to have the name given by DECL_NAME. In some cases, there is no associated name.
These nodes represent variables with namespace or block scope, as well as static data members. The DECL_SIZE and DECL_ALIGN are analogous to TYPE_SIZE and TYPE_ALIGN. For a declaration, you should always use the DECL_SIZE and DECL_ALIGN rather than the TYPE_SIZE and TYPE_ALIGN given by the TREE_TYPE, since special attributes may have been applied to the variable to give it a particular size and alignment. You may use the predicates DECL_THIS_STATIC or DECL_THIS_EXTERN to test whether the storage class specifiers static or extern were used to declare a variable.

If this variable is initialized (but does not require a constructor), the DECL_INITIAL will be an expression for the initializer. The initializer should be evaluated, and a bitwise copy into the variable performed. If the DECL_INITIAL is the error_mark_node, there is an initializer, but it is given by an explicit statement later in the code; no bitwise copy is required.

GCC provides an extension that allows either automatic variables, or global variables, to be placed in particular registers. This extension is being used for a particular VAR_DECL if DECL_REGISTER holds for the VAR_DECL, and if DECL_ASSEMBLER_NAME is not equal to DECL_NAME. In that case, DECL_ASSEMBLER_NAME is the name of the register into which the variable will be placed.

Used to represent a parameter to a function. Treat these nodes similarly to VAR_DECL nodes. These nodes only appear in the DECL_ARGUMENTS for a FUNCTION_DECL.

The DECL_ARG_TYPE for a PARM_DECL is the type that will actually be used when a value is passed to this function. It may be a wider type than the TREE_TYPE of the parameter; for example, the ordinary type might be short while the DECL_ARG_TYPE is int.

These nodes represent non-static data members. The DECL_SIZE and DECL_ALIGN behave as for VAR_DECL nodes. The DECL_FIELD_BITPOS gives the first bit used for this field, as an INTEGER_CST. These values are indexed from zero, where zero indicates the first bit in the object.

If DECL_C_BIT_FIELD holds, this field is a bit-field.

See Namespaces.
These nodes are used to represent class, function, and variable (static data member) templates. The DECL_TEMPLATE_SPECIALIZATIONS are a TREE_LIST. The TREE_VALUE of each node in the list is a TEMPLATE_DECLs or FUNCTION_DECLs representing specializations (including instantiations) of this template. Back ends can safely ignore TEMPLATE_DECLs, but should examine FUNCTION_DECL nodes on the specializations list just as they would ordinary FUNCTION_DECL nodes.

For a class template, the DECL_TEMPLATE_INSTANTIATIONS list contains the instantiations. The TREE_VALUE of each node is an instantiation of the class. The DECL_TEMPLATE_SPECIALIZATIONS contains partial specializations of the class.

Back ends can safely ignore these nodes.