The Tcpdump Group git mirrors - libpcap/blob - missing/asprintf.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <stdarg.h>
   4
   5 #include "portability.h"
   6
   7 /*
   8  * vasprintf() and asprintf() for platforms with a C99-compliant
   9  * snprintf() - so that, if you format into a 1-byte buffer, it
  10  * will return how many characters it would have produced had
  11  * it been given an infinite-sized buffer.
  12  */
  13 int
  14 pcapint_vasprintf(char **strp, const char *format, va_list args)
  15 {
  16         char buf;
  17         int len;
  18         size_t str_size;
  19         char *str;
  20         int ret;
  21
  22         /*
  23          * XXX - the C99 standard says, in section 7.19.6.5 "The
  24          * snprintf function":
  25          *
  26          *    The snprintf function is equivalent to fprintf, except that
  27          *    the output is written into an array (specified by argument s)
  28          *    rather than to a stream.  If n is zero, nothing is written,
  29          *    and s may be a null pointer.  Otherwise, output characters
  30          *    beyond the n-1st are discarded rather than being written
  31          *    to the array, and a null character is written at the end
  32          *    of the characters actually written into the array.
  33          *
  34          *        ...
  35          *
  36          *    The snprintf function returns the number of characters that
  37          *    would have been written had n been sufficiently large, not
  38          *    counting the terminating null character, or a negative value
  39          *    if an encoding error occurred. Thus, the null-terminated
  40          *    output has been completely written if and only if the returned
  41          *    value is nonnegative and less than n.
  42          *
  43          * That doesn't make it entirely clear whether, if a null buffer
  44          * pointer and a zero count are passed, it will return the number
  45          * of characters that would have been written had a buffer been
  46          * passed.
  47          *
  48          * And, even if C99 *does*, in fact, say it has to work, it
  49          * doesn't work in Solaris 8, for example - it returns -1 for
  50          * NULL/0, but returns the correct character count for a 1-byte
  51          * buffer.
  52          *
  53          * So we pass a one-character pointer in order to find out how
  54          * many characters this format and those arguments will need
  55          * without actually generating any more of those characters
  56          * than we need.
  57          *
  58          * (The fact that it might happen to work with GNU libc or with
  59          * various BSD libcs is completely uninteresting, as those tend
  60          * to have asprintf() already and thus don't even *need* this
  61          * code; this is for use in those UN*Xes that *don't* have
  62          * asprintf().)
  63          */
  64         len = vsnprintf(&buf, sizeof buf, format, args);
  65         if (len == -1) {
  66                 *strp = NULL;
  67                 return (-1);
  68         }
  69         str_size = len + 1;
  70         str = malloc(str_size);
  71         if (str == NULL) {
  72                 *strp = NULL;
  73                 return (-1);
  74         }
  75         ret = vsnprintf(str, str_size, format, args);
  76         if (ret == -1) {
  77                 free(str);
  78                 *strp = NULL;
  79                 return (-1);
  80         }
  81         *strp = str;
  82         /*
  83          * vsnprintf() shouldn't truncate the string, as we have
  84          * allocated a buffer large enough to hold the string, so its
  85          * return value should be the number of characters written.
  86          */
  87         return (ret);
  88 }
  89
  90 int
  91 pcapint_asprintf(char **strp, const char *format, ...)
  92 {
  93         va_list args;
  94         int ret;
  95
  96         va_start(args, format);
  97         ret = pcapint_vasprintf(strp, format, args);
  98         va_end(args);
  99         return (ret);
 100 }
 101