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<title>GNU Compiler Collection (GCC) Internals: Working with declarations</title>
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<a name="Working-with-declarations"></a>
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<div class="header">
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<p>
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Next: <a href="Internal-structure.html#Internal-structure" accesskey="n" rel="next">Internal structure</a>, Up: <a href="Declarations.html#Declarations" accesskey="u" rel="up">Declarations</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Working-with-declarations-1"></a>
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<h4 class="subsection">10.4.1 Working with declarations</h4>
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<p>Some macros can be used with any kind of declaration. These include:
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</p><dl compact="compact">
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<dt><code>DECL_NAME</code>
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<a name="index-DECL_005fNAME"></a>
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</dt>
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<dd><p>This macro returns an <code>IDENTIFIER_NODE</code> giving the name of the
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entity.
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</p>
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</dd>
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<dt><code>TREE_TYPE</code>
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<a name="index-TREE_005fTYPE-2"></a>
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</dt>
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<dd><p>This macro returns the type of the entity declared.
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</p>
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</dd>
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<dt><code>EXPR_FILENAME</code>
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<a name="index-EXPR_005fFILENAME"></a>
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</dt>
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<dd><p>This macro returns the name of the file in which the entity was
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declared, as a <code>char*</code>. For an entity declared implicitly by the
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compiler (like <code>__builtin_memcpy</code>), this will be the string
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<code>"<internal>"</code>.
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</p>
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</dd>
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<dt><code>EXPR_LINENO</code>
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<a name="index-EXPR_005fLINENO"></a>
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</dt>
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<dd><p>This macro returns the line number at which the entity was declared, as
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an <code>int</code>.
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</p>
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</dd>
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<dt><code>DECL_ARTIFICIAL</code>
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<a name="index-DECL_005fARTIFICIAL"></a>
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</dt>
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<dd><p>This predicate holds if the declaration was implicitly generated by the
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compiler. For example, this predicate will hold of an implicitly
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declared member function, or of the <code>TYPE_DECL</code> implicitly
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generated for a class type. Recall that in C++ code like:
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</p><div class="smallexample">
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<pre class="smallexample">struct S {};
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</pre></div>
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<p>is roughly equivalent to C code like:
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</p><div class="smallexample">
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<pre class="smallexample">struct S {};
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typedef struct S S;
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</pre></div>
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<p>The implicitly generated <code>typedef</code> declaration is represented by a
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<code>TYPE_DECL</code> for which <code>DECL_ARTIFICIAL</code> holds.
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</p>
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</dd>
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</dl>
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<p>The various kinds of declarations include:
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</p><dl compact="compact">
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<dt><code>LABEL_DECL</code></dt>
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<dd><p>These nodes are used to represent labels in function bodies. For more
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information, see <a href="Functions.html#Functions">Functions</a>. These nodes only appear in block
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scopes.
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</p>
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</dd>
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<dt><code>CONST_DECL</code></dt>
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<dd><p>These nodes are used to represent enumeration constants. The value of
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the constant is given by <code>DECL_INITIAL</code> which will be an
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<code>INTEGER_CST</code> with the same type as the <code>TREE_TYPE</code> of the
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<code>CONST_DECL</code>, i.e., an <code>ENUMERAL_TYPE</code>.
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</p>
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</dd>
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<dt><code>RESULT_DECL</code></dt>
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<dd><p>These nodes represent the value returned by a function. When a value is
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assigned to a <code>RESULT_DECL</code>, that indicates that the value should
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be returned, via bitwise copy, by the function. You can use
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<code>DECL_SIZE</code> and <code>DECL_ALIGN</code> on a <code>RESULT_DECL</code>, just as
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with a <code>VAR_DECL</code>.
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</p>
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</dd>
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<dt><code>TYPE_DECL</code></dt>
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<dd><p>These nodes represent <code>typedef</code> declarations. The <code>TREE_TYPE</code>
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is the type declared to have the name given by <code>DECL_NAME</code>. In
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some cases, there is no associated name.
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</p>
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</dd>
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<dt><code>VAR_DECL</code></dt>
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<dd><p>These nodes represent variables with namespace or block scope, as well
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as static data members. The <code>DECL_SIZE</code> and <code>DECL_ALIGN</code> are
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analogous to <code>TYPE_SIZE</code> and <code>TYPE_ALIGN</code>. For a declaration,
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you should always use the <code>DECL_SIZE</code> and <code>DECL_ALIGN</code> rather
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than the <code>TYPE_SIZE</code> and <code>TYPE_ALIGN</code> given by the
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<code>TREE_TYPE</code>, since special attributes may have been applied to the
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variable to give it a particular size and alignment. You may use the
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predicates <code>DECL_THIS_STATIC</code> or <code>DECL_THIS_EXTERN</code> to test
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whether the storage class specifiers <code>static</code> or <code>extern</code> were
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used to declare a variable.
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</p>
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<p>If this variable is initialized (but does not require a constructor),
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the <code>DECL_INITIAL</code> will be an expression for the initializer. The
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initializer should be evaluated, and a bitwise copy into the variable
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performed. If the <code>DECL_INITIAL</code> is the <code>error_mark_node</code>,
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there is an initializer, but it is given by an explicit statement later
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in the code; no bitwise copy is required.
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</p>
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<p>GCC provides an extension that allows either automatic variables, or
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global variables, to be placed in particular registers. This extension
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is being used for a particular <code>VAR_DECL</code> if <code>DECL_REGISTER</code>
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holds for the <code>VAR_DECL</code>, and if <code>DECL_ASSEMBLER_NAME</code> is not
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equal to <code>DECL_NAME</code>. In that case, <code>DECL_ASSEMBLER_NAME</code> is
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the name of the register into which the variable will be placed.
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</p>
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</dd>
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<dt><code>PARM_DECL</code></dt>
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<dd><p>Used to represent a parameter to a function. Treat these nodes
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similarly to <code>VAR_DECL</code> nodes. These nodes only appear in the
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<code>DECL_ARGUMENTS</code> for a <code>FUNCTION_DECL</code>.
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</p>
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<p>The <code>DECL_ARG_TYPE</code> for a <code>PARM_DECL</code> is the type that will
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actually be used when a value is passed to this function. It may be a
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wider type than the <code>TREE_TYPE</code> of the parameter; for example, the
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ordinary type might be <code>short</code> while the <code>DECL_ARG_TYPE</code> is
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<code>int</code>.
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</p>
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</dd>
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<dt><code>DEBUG_EXPR_DECL</code></dt>
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<dd><p>Used to represent an anonymous debug-information temporary created to
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hold an expression as it is optimized away, so that its value can be
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referenced in debug bind statements.
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</p>
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</dd>
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<dt><code>FIELD_DECL</code></dt>
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<dd><p>These nodes represent non-static data members. The <code>DECL_SIZE</code> and
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<code>DECL_ALIGN</code> behave as for <code>VAR_DECL</code> nodes.
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The position of the field within the parent record is specified by a
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combination of three attributes. <code>DECL_FIELD_OFFSET</code> is the position,
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counting in bytes, of the <code>DECL_OFFSET_ALIGN</code>-bit sized word containing
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the bit of the field closest to the beginning of the structure.
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<code>DECL_FIELD_BIT_OFFSET</code> is the bit offset of the first bit of the field
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within this word; this may be nonzero even for fields that are not bit-fields,
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since <code>DECL_OFFSET_ALIGN</code> may be greater than the natural alignment
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of the field’s type.
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</p>
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<p>If <code>DECL_C_BIT_FIELD</code> holds, this field is a bit-field. In a bit-field,
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<code>DECL_BIT_FIELD_TYPE</code> also contains the type that was originally
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specified for it, while DECL_TYPE may be a modified type with lesser precision,
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according to the size of the bit field.
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</p>
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</dd>
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<dt><code>NAMESPACE_DECL</code></dt>
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<dd><p>Namespaces provide a name hierarchy for other declarations. They
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appear in the <code>DECL_CONTEXT</code> of other <code>_DECL</code> nodes.
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</p>
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</dd>
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</dl>
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Next: <a href="Internal-structure.html#Internal-structure" accesskey="n" rel="next">Internal structure</a>, Up: <a href="Declarations.html#Declarations" accesskey="u" rel="up">Declarations</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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