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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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