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<h5 class="subsubsection">3.2.2.3 Freeing Memory Allocated with <code>malloc</code></h5>

<p><a name="index-freeing-memory-allocated-with-_0040code_007bmalloc_007d-260"></a><a name="index-heap_002c-freeing-memory-from-261"></a>
When you no longer need a block that you got with <code>malloc</code>, use the
function <code>free</code> to make the block available to be allocated again. 
The prototype for this function is in <samp><span class="file">stdlib.h</span></samp>. 
<a name="index-stdlib_002eh-262"></a>
<!-- malloc.h stdlib.h -->
<!-- ISO -->

<div class="defun">
&mdash; Function: void <b>free</b> (<var>void *ptr</var>)<var><a name="index-free-263"></a></var><br>
<blockquote><p>The <code>free</code> function deallocates the block of memory pointed at
by <var>ptr</var>. 
</p></blockquote></div>

<!-- stdlib.h -->
<!-- Sun -->
<div class="defun">
&mdash; Function: void <b>cfree</b> (<var>void *ptr</var>)<var><a name="index-cfree-264"></a></var><br>
<blockquote><p>This function does the same thing as <code>free</code>.  It's provided for
backward compatibility with SunOS; you should use <code>free</code> instead. 
</p></blockquote></div>

   <p>Freeing a block alters the contents of the block.  <strong>Do not expect to
find any data (such as a pointer to the next block in a chain of blocks) in
the block after freeing it.</strong>  Copy whatever you need out of the block before
freeing it!  Here is an example of the proper way to free all the blocks in
a chain, and the strings that they point to:

<pre class="smallexample">     struct chain
       {
         struct chain *next;
         char *name;
       }
     
     void
     free_chain (struct chain *chain)
     {
       while (chain != 0)
         {
           struct chain *next = chain-&gt;next;
           free (chain-&gt;name);
           free (chain);
           chain = next;
         }
     }
</pre>
   <p>Occasionally, <code>free</code> can actually return memory to the operating
system and make the process smaller.  Usually, all it can do is allow a
later call to <code>malloc</code> to reuse the space.  In the meantime, the
space remains in your program as part of a free-list used internally by
<code>malloc</code>.

   <p>There is no point in freeing blocks at the end of a program, because all
of the program's space is given back to the system when the process
terminates.

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