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(libc.info)Alloca Example


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`alloca' Example
................

   As an example of the use of `alloca', 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:

     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);
     }

Here is how you would get the same results with `malloc' and `free':

     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;
     }

   As you can see, it is simpler with `alloca'.  But `alloca' has
other, more important advantages, and some disadvantages.


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