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<title>GNU Compiler Collection (GCC) Internals: Working with declarations</title>

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<a name="Working-with-declarations"></a>
<div class="header">
<p>
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> &nbsp; [<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>
</div>
<hr>
<a name="Working-with-declarations-1"></a>
<h4 class="subsection">10.4.1 Working with declarations</h4>

<p>Some macros can be used with any kind of declaration.  These include:
</p><dl compact="compact">
<dt><code>DECL_NAME</code>
<a name="index-DECL_005fNAME"></a>
</dt>
<dd><p>This macro returns an <code>IDENTIFIER_NODE</code> giving the name of the
entity.
</p>
</dd>
<dt><code>TREE_TYPE</code>
<a name="index-TREE_005fTYPE-2"></a>
</dt>
<dd><p>This macro returns the type of the entity declared.
</p>
</dd>
<dt><code>EXPR_FILENAME</code>
<a name="index-EXPR_005fFILENAME"></a>
</dt>
<dd><p>This macro returns the name of the file in which the entity was
declared, as a <code>char*</code>.  For an entity declared implicitly by the
compiler (like <code>__builtin_memcpy</code>), this will be the string
<code>&quot;&lt;internal&gt;&quot;</code>.
</p>
</dd>
<dt><code>EXPR_LINENO</code>
<a name="index-EXPR_005fLINENO"></a>
</dt>
<dd><p>This macro returns the line number at which the entity was declared, as
an <code>int</code>.
</p>
</dd>
<dt><code>DECL_ARTIFICIAL</code>
<a name="index-DECL_005fARTIFICIAL"></a>
</dt>
<dd><p>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 <code>TYPE_DECL</code> implicitly
generated for a class type.  Recall that in C++ code like:
</p><div class="smallexample">
<pre class="smallexample">struct S {};
</pre></div>
<p>is roughly equivalent to C code like:
</p><div class="smallexample">
<pre class="smallexample">struct S {};
typedef struct S S;
</pre></div>
<p>The implicitly generated <code>typedef</code> declaration is represented by a
<code>TYPE_DECL</code> for which <code>DECL_ARTIFICIAL</code> holds.
</p>
</dd>
</dl>

<p>The various kinds of declarations include:
</p><dl compact="compact">
<dt><code>LABEL_DECL</code></dt>
<dd><p>These nodes are used to represent labels in function bodies.  For more
information, see <a href="Functions.html#Functions">Functions</a>.  These nodes only appear in block
scopes.
</p>
</dd>
<dt><code>CONST_DECL</code></dt>
<dd><p>These nodes are used to represent enumeration constants.  The value of
the constant is given by <code>DECL_INITIAL</code> which will be an
<code>INTEGER_CST</code> with the same type as the <code>TREE_TYPE</code> of the
<code>CONST_DECL</code>, i.e., an <code>ENUMERAL_TYPE</code>.
</p>
</dd>
<dt><code>RESULT_DECL</code></dt>
<dd><p>These nodes represent the value returned by a function.  When a value is
assigned to a <code>RESULT_DECL</code>, that indicates that the value should
be returned, via bitwise copy, by the function.  You can use
<code>DECL_SIZE</code> and <code>DECL_ALIGN</code> on a <code>RESULT_DECL</code>, just as
with a <code>VAR_DECL</code>.
</p>
</dd>
<dt><code>TYPE_DECL</code></dt>
<dd><p>These nodes represent <code>typedef</code> declarations.  The <code>TREE_TYPE</code>
is the type declared to have the name given by <code>DECL_NAME</code>.  In
some cases, there is no associated name.
</p>
</dd>
<dt><code>VAR_DECL</code></dt>
<dd><p>These nodes represent variables with namespace or block scope, as well
as static data members.  The <code>DECL_SIZE</code> and <code>DECL_ALIGN</code> are
analogous to <code>TYPE_SIZE</code> and <code>TYPE_ALIGN</code>.  For a declaration,
you should always use the <code>DECL_SIZE</code> and <code>DECL_ALIGN</code> rather
than the <code>TYPE_SIZE</code> and <code>TYPE_ALIGN</code> given by the
<code>TREE_TYPE</code>, since special attributes may have been applied to the
variable to give it a particular size and alignment.  You may use the
predicates <code>DECL_THIS_STATIC</code> or <code>DECL_THIS_EXTERN</code> to test
whether the storage class specifiers <code>static</code> or <code>extern</code> were
used to declare a variable.
</p>
<p>If this variable is initialized (but does not require a constructor),
the <code>DECL_INITIAL</code> will be an expression for the initializer.  The
initializer should be evaluated, and a bitwise copy into the variable
performed.  If the <code>DECL_INITIAL</code> is the <code>error_mark_node</code>,
there is an initializer, but it is given by an explicit statement later
in the code; no bitwise copy is required.
</p>
<p>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 <code>VAR_DECL</code> if <code>DECL_REGISTER</code>
holds for the <code>VAR_DECL</code>, and if <code>DECL_ASSEMBLER_NAME</code> is not
equal to <code>DECL_NAME</code>.  In that case, <code>DECL_ASSEMBLER_NAME</code> is
the name of the register into which the variable will be placed.
</p>
</dd>
<dt><code>PARM_DECL</code></dt>
<dd><p>Used to represent a parameter to a function.  Treat these nodes
similarly to <code>VAR_DECL</code> nodes.  These nodes only appear in the
<code>DECL_ARGUMENTS</code> for a <code>FUNCTION_DECL</code>.
</p>
<p>The <code>DECL_ARG_TYPE</code> for a <code>PARM_DECL</code> is the type that will
actually be used when a value is passed to this function.  It may be a
wider type than the <code>TREE_TYPE</code> of the parameter; for example, the
ordinary type might be <code>short</code> while the <code>DECL_ARG_TYPE</code> is
<code>int</code>.
</p>
</dd>
<dt><code>DEBUG_EXPR_DECL</code></dt>
<dd><p>Used to represent an anonymous debug-information temporary created to
hold an expression as it is optimized away, so that its value can be
referenced in debug bind statements.
</p>
</dd>
<dt><code>FIELD_DECL</code></dt>
<dd><p>These nodes represent non-static data members.  The <code>DECL_SIZE</code> and
<code>DECL_ALIGN</code> behave as for <code>VAR_DECL</code> nodes.
The position of the field within the parent record is specified by a
combination of three attributes.  <code>DECL_FIELD_OFFSET</code> is the position,
counting in bytes, of the <code>DECL_OFFSET_ALIGN</code>-bit sized word containing
the bit of the field closest to the beginning of the structure.
<code>DECL_FIELD_BIT_OFFSET</code> is the bit offset of the first bit of the field
within this word; this may be nonzero even for fields that are not bit-fields,
since <code>DECL_OFFSET_ALIGN</code> may be greater than the natural alignment
of the field&rsquo;s type.
</p>
<p>If <code>DECL_C_BIT_FIELD</code> holds, this field is a bit-field.  In a bit-field,
<code>DECL_BIT_FIELD_TYPE</code> also contains the type that was originally
specified for it, while DECL_TYPE may be a modified type with lesser precision,
according to the size of the bit field.
</p>
</dd>
<dt><code>NAMESPACE_DECL</code></dt>
<dd><p>Namespaces provide a name hierarchy for other declarations.  They
appear in the <code>DECL_CONTEXT</code> of other <code>_DECL</code> nodes.
</p>
</dd>
</dl>

<hr>
<div class="header">
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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> &nbsp; [<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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