citadel/snprintf.c

   1 /*
   2  * $Id$
   3  *
   4  * Replacements for snprintf() and vsnprintf()
   5  *
   6  * modified from Sten Gunterberg's BUGTRAQ post of 22 Jul 1997
   7  * --nathan bryant <nathan@designtrust.com>
   8  *
   9  * Use it only if you have the "spare" cycles needed to effectively
  10  * do every snprintf operation twice! Why is that? Because everything
  11  * is first vfprintf()'d to /dev/null to determine the number of bytes.
  12  * Perhaps a bit slow for demanding applications on slow machines,
  13  * no problem for a fast machine with some spare cycles.
  14  *
  15  * You don't have a /dev/null? Every Linux contains one for free!
  16  *
  17  * Because the format string is never even looked at, all current and
  18  * possible future printf-conversions should be handled just fine.
  19  *
  20  * Written July 1997 by Sten Gunterberg (gunterberg@ergon.ch)
  21  */
  22
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <stdarg.h>
  26 #include <string.h>
  27
  28 static int
  29 needed (const char *fmt, va_list argp)
  30 {
  31   static FILE *sink = NULL;
  32
  33   /* ok, there's a small race here that could result in the sink being
  34    * opened more than once if we're threaded, but I'd rather ignore it than
  35    * spend cycles synchronizing :-) */
  36
  37   if (sink == NULL)
  38     {
  39       if ((sink = fopen("/dev/null", "w")) == NULL)
  40         {
  41           perror("/dev/null");
  42           exit(1);
  43         }
  44     }
  45
  46   return vfprintf(sink, fmt, argp);
  47 }
  48
  49 int
  50 vsnprintf (char *buf, size_t max, const char *fmt, va_list argp)
  51 {
  52   char *p;
  53   int size;
  54
  55   if ((p = malloc(needed(fmt, argp) + 1)) == NULL)
  56     {
  57       fprintf(stderr, "vsnprintf: malloc failed, aborting\n");
  58       abort();
  59     }
  60
  61   if ((size = vsprintf(p, fmt, argp)) >= max)
  62     size = -1;
  63
  64   strncpy(buf, p, max);
  65   buf[max - 1] = 0;
  66   free(p);
  67   return size;
  68 }
  69
  70 int
  71 snprintf (char *buf, size_t max, const char *fmt, ...)
  72 {
  73   va_list argp;
  74   int bytes;
  75
  76   va_start(argp, fmt);
  77   bytes = vsnprintf(buf, max, fmt, argp);
  78   va_end(argp);
  79
  80   return bytes;
  81 }