/*
* vasprintf() and asprintf() for platforms with a C99-compliant
* snprintf() - so that, if you format into a 1-byte buffer, it
* will return how many characters it would have produced had
* it been given an infinite-sized buffer.
*/
int
pcapint_vasprintf(char **strp, const char *format, va_list args)
{
char buf;
int len;
size_t str_size;
char *str;
int ret;
/*
* XXX - the C99 standard says, in section 7.19.6.5 "The
* snprintf function":
*
* The snprintf function is equivalent to fprintf, except that
* the output is written into an array (specified by argument s)
* rather than to a stream. If n is zero, nothing is written,
* and s may be a null pointer. Otherwise, output characters
* beyond the n-1st are discarded rather than being written
* to the array, and a null character is written at the end
* of the characters actually written into the array.
*
* ...
*
* The snprintf function returns the number of characters that
* would have been written had n been sufficiently large, not
* counting the terminating null character, or a negative value
* if an encoding error occurred. Thus, the null-terminated
* output has been completely written if and only if the returned
* value is nonnegative and less than n.
*
* That doesn't make it entirely clear whether, if a null buffer
* pointer and a zero count are passed, it will return the number
* of characters that would have been written had a buffer been
* passed.
*
* And, even if C99 *does*, in fact, say it has to work, it
* doesn't work in Solaris 8, for example - it returns -1 for
* NULL/0, but returns the correct character count for a 1-byte
* buffer.
*
* So we pass a one-character pointer in order to find out how
* many characters this format and those arguments will need
* without actually generating any more of those characters
* than we need.
*
* (The fact that it might happen to work with GNU libc or with
* various BSD libcs is completely uninteresting, as those tend
* to have asprintf() already and thus don't even *need* this
* code; this is for use in those UN*Xes that *don't* have
* asprintf().)
*/
len = vsnprintf(&buf, sizeof buf, format, args);
if (len == -1) {
*strp = NULL;
return (-1);
}
str_size = len + 1;
str = malloc(str_size);
if (str == NULL) {
*strp = NULL;
return (-1);
}
ret = vsnprintf(str, str_size, format, args);
if (ret == -1) {
free(str);
*strp = NULL;
return (-1);
}
*strp = str;
/*
* vsnprintf() shouldn't truncate the string, as we have
* allocated a buffer large enough to hold the string, so its
* return value should be the number of characters written.
*/
return (ret);
}
int
pcapint_asprintf(char **strp, const char *format, ...)
{
va_list args;
int ret;
va_start(args, format);
ret = pcapint_vasprintf(strp, format, args);
va_end(args);
return (ret);
}
