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 <p>
 Next:&nbsp;<a rel="next" accesskey="n" href="Allocation-in-an-Obstack.html#Allocation-in-an-Obstack">Allocation in an Obstack</a>,
 Previous:&nbsp;<a rel="previous" accesskey="p" href="Creating-Obstacks.html#Creating-Obstacks">Creating Obstacks</a>,
 Up:&nbsp;<a rel="up" accesskey="u" href="Obstacks.html#Obstacks">Obstacks</a>
 <hr>
 </div>

 <h5 class="subsubsection">3.2.4.2 Preparing for Using Obstacks</h5>

 <p>Each source file in which you plan to use the obstack functions
 must include the header file <samp><span class="file">obstack.h</span></samp>, like this:

 <pre class="smallexample">     #include &lt;obstack.h&gt;
 </pre>
    <p><a name="index-obstack_005fchunk_005falloc-303"></a><a name="index-obstack_005fchunk_005ffree-304"></a>Also, if the source file uses the macro <code>obstack_init</code>, it must
 declare or define two functions or macros that will be called by the
 obstack library.  One, <code>obstack_chunk_alloc</code>, is used to allocate
 the chunks of memory into which objects are packed.  The other,
 <code>obstack_chunk_free</code>, is used to return chunks when the objects in
 them are freed.  These macros should appear before any use of obstacks
 in the source file.

    <p>Usually these are defined to use <code>malloc</code> via the intermediary
 <code>xmalloc</code> (see <a href="Unconstrained-Allocation.html#Unconstrained-Allocation">Unconstrained Allocation</a>).  This is done with
 the following pair of macro definitions:

 <pre class="smallexample">     #define obstack_chunk_alloc xmalloc
      #define obstack_chunk_free free
 </pre>
    <p class="noindent">Though the memory you get using obstacks really comes from <code>malloc</code>,
 using obstacks is faster because <code>malloc</code> is called less often, for
 larger blocks of memory.  See <a href="Obstack-Chunks.html#Obstack-Chunks">Obstack Chunks</a>, for full details.

    <p>At run time, before the program can use a <code>struct obstack</code> object
 as an obstack, it must initialize the obstack by calling
 <code>obstack_init</code>.

 <!-- obstack.h -->
 <!-- GNU -->
 <div class="defun">
 &mdash; Function: int <b>obstack_init</b> (<var>struct obstack *obstack-ptr</var>)<var><a name="index-obstack_005finit-305"></a></var><br>
 <blockquote><p>Initialize obstack <var>obstack-ptr</var> for allocation of objects.  This
 function calls the obstack's <code>obstack_chunk_alloc</code> function.  If
 allocation of memory fails, the function pointed to by
 <code>obstack_alloc_failed_handler</code> is called.  The <code>obstack_init</code>
 function always returns 1 (Compatibility notice: Former versions of
 obstack returned 0 if allocation failed).
 </p></blockquote></div>

    <p>Here are two examples of how to allocate the space for an obstack and
 initialize it.  First, an obstack that is a static variable:

 <pre class="smallexample">     static struct obstack myobstack;
      ...
      obstack_init (&amp;myobstack);
 </pre>
    <p class="noindent">Second, an obstack that is itself dynamically allocated:

 <pre class="smallexample">     struct obstack *myobstack_ptr
        = (struct obstack *) xmalloc (sizeof (struct obstack));

      obstack_init (myobstack_ptr);
 </pre>
    <!-- obstack.h -->
 <!-- GNU -->
 <div class="defun">
 &mdash; Variable: <b>obstack_alloc_failed_handler</b><var><a name="index-obstack_005falloc_005ffailed_005fhandler-306"></a></var><br>
 <blockquote><p>The value of this variable is a pointer to a function that
 <code>obstack</code> uses when <code>obstack_chunk_alloc</code> fails to allocate
 memory.  The default action is to print a message and abort.
 You should supply a function that either calls <code>exit</code>
 (see <a href="Program-Termination.html#Program-Termination">Program Termination</a>) or <code>longjmp</code> (see <a href="Non_002dLocal-Exits.html#Non_002dLocal-Exits">Non-Local Exits</a>) and doesn't return.

      <pre class="smallexample">          void my_obstack_alloc_failed (void)
           ...
           obstack_alloc_failed_handler = &amp;my_obstack_alloc_failed;
 </pre>
         </blockquote></div>

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	<p>
	Next: <a rel="next" accesskey="n" href="Allocation-in-an-Obstack.html#Allocation-in-an-Obstack">Allocation in an Obstack</a>,
	Previous: <a rel="previous" accesskey="p" href="Creating-Obstacks.html#Creating-Obstacks">Creating Obstacks</a>,
	Up: <a rel="up" accesskey="u" href="Obstacks.html#Obstacks">Obstacks</a>
	<hr>
	</div>

	<h5 class="subsubsection">3.2.4.2 Preparing for Using Obstacks</h5>

	<p>Each source file in which you plan to use the obstack functions
	must include the header file <samp><span class="file">obstack.h</span></samp>, like this:

	<pre class="smallexample"> #include <obstack.h>
	</pre>
	<p><a name="index-obstack_005fchunk_005falloc-303"></a><a name="index-obstack_005fchunk_005ffree-304"></a>Also, if the source file uses the macro <code>obstack_init</code>, it must
	declare or define two functions or macros that will be called by the
	obstack library. One, <code>obstack_chunk_alloc</code>, is used to allocate
	the chunks of memory into which objects are packed. The other,
	<code>obstack_chunk_free</code>, is used to return chunks when the objects in
	them are freed. These macros should appear before any use of obstacks
	in the source file.

	<p>Usually these are defined to use <code>malloc</code> via the intermediary
	<code>xmalloc</code> (see <a href="Unconstrained-Allocation.html#Unconstrained-Allocation">Unconstrained Allocation</a>). This is done with
	the following pair of macro definitions:

	<pre class="smallexample"> #define obstack_chunk_alloc xmalloc
	#define obstack_chunk_free free
	</pre>
	<p class="noindent">Though the memory you get using obstacks really comes from <code>malloc</code>,
	using obstacks is faster because <code>malloc</code> is called less often, for
	larger blocks of memory. See <a href="Obstack-Chunks.html#Obstack-Chunks">Obstack Chunks</a>, for full details.

	<p>At run time, before the program can use a <code>struct obstack</code> object
	as an obstack, it must initialize the obstack by calling
	<code>obstack_init</code>.

	<!-- obstack.h -->
	<!-- GNU -->
	<div class="defun">
	— Function: int <b>obstack_init</b> (<var>struct obstack *obstack-ptr</var>)<var><a name="index-obstack_005finit-305"></a></var><br>
	<blockquote><p>Initialize obstack <var>obstack-ptr</var> for allocation of objects. This
	function calls the obstack's <code>obstack_chunk_alloc</code> function. If
	allocation of memory fails, the function pointed to by
	<code>obstack_alloc_failed_handler</code> is called. The <code>obstack_init</code>
	function always returns 1 (Compatibility notice: Former versions of
	obstack returned 0 if allocation failed).
	</p></blockquote></div>

	<p>Here are two examples of how to allocate the space for an obstack and
	initialize it. First, an obstack that is a static variable:

	<pre class="smallexample"> static struct obstack myobstack;
	...
	obstack_init (&myobstack);
	</pre>
	<p class="noindent">Second, an obstack that is itself dynamically allocated:

	<pre class="smallexample"> struct obstack *myobstack_ptr
	= (struct obstack *) xmalloc (sizeof (struct obstack));

	obstack_init (myobstack_ptr);
	</pre>
	<!-- obstack.h -->
	<!-- GNU -->
	<div class="defun">
	— Variable: <b>obstack_alloc_failed_handler</b><var><a name="index-obstack_005falloc_005ffailed_005fhandler-306"></a></var><br>
	<blockquote><p>The value of this variable is a pointer to a function that
	<code>obstack</code> uses when <code>obstack_chunk_alloc</code> fails to allocate
	memory. The default action is to print a message and abort.
	You should supply a function that either calls <code>exit</code>
	(see <a href="Program-Termination.html#Program-Termination">Program Termination</a>) or <code>longjmp</code> (see <a href="Non_002dLocal-Exits.html#Non_002dLocal-Exits">Non-Local Exits</a>) and doesn't return.

	<pre class="smallexample"> void my_obstack_alloc_failed (void)
	...
	obstack_alloc_failed_handler = &my_obstack_alloc_failed;
	</pre>
	</blockquote></div>

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