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alloca
ExampleAs 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.