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<title>Alloca Example - The GNU C Library</title>
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<h5 class="subsubsection">3.2.5.1 <code>alloca</code> Example</h5>

<p>As an example of the use of <code>alloca</code>, here is a function that opens
a file name made from concatenating two argument strings, and returns a
file descriptor or minus one signifying failure:

<pre class="smallexample">     int
     open2 (char *str1, char *str2, int flags, int mode)
     {
       char *name = (char *) alloca (strlen (str1) + strlen (str2) + 1);
       stpcpy (stpcpy (name, str1), str2);
       return open (name, flags, mode);
     }
</pre>
   <p class="noindent">Here is how you would get the same results with <code>malloc</code> and
<code>free</code>:

<pre class="smallexample">     int
     open2 (char *str1, char *str2, int flags, int mode)
     {
       char *name = (char *) malloc (strlen (str1) + strlen (str2) + 1);
       int desc;
       if (name == 0)
         fatal ("virtual memory exceeded");
       stpcpy (stpcpy (name, str1), str2);
       desc = open (name, flags, mode);
       free (name);
       return desc;
     }
</pre>
   <p>As you can see, it is simpler with <code>alloca</code>.  But <code>alloca</code> has
other, more important advantages, and some disadvantages.

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