Something like this (C99; given p, stack-allocates p_sasprintf_buf of size at most 16 if the string would fit, and uses asprintf otherwise): #include <err.

Something like this (C99; given p, stack-allocates p_sasprintf_buf of size at most 16 if the string would fit, and uses asprintf otherwise): #include <err.h> #include <stdio.h> #include <stdlib.h> #define SASPRINTF_MAXLEN 16 #define SASPRINTF_MERGE(a, b) a ## b #define SASPRINTF_LEN(p) SASPRINTF_MERGE(p, _sasprintf_len) #define SASPRINTF_BUF(p) SASPRINTF_MERGE(p, _sasprintf_buf) #define SASPRINTF(p, fmt, ...) \ size_t SASPRINTF_LEN(p) = snprintf(NULL, 0, (fmt), __VA_ARGS__); \ char SASPRINTF_BUF(p)[SASPRINTF_LEN(p) <= SASPRINTF_MAXLEN ? SASPRINTF_LEN(p) + 1 : 0]; \ if (SASPRINTF_LEN(p) <= SASPRINTF_MAXLEN) { \ snprintf(SASPRINTF_BUF(p), SASPRINTF_LEN(p) + 1, (fmt), __VA_ARGS__); \ p = SASPRINTF_BUF(p); \ } else { \ if (asprintf(&p, (fmt), __VA_ARGS__) == -1) \ err(1, "SASPRINTF_L at %s, %d", __FILE__, __LINE__); \ } #define SASPRINTF_FREE(p) do { \ if (p != SASPRINTF_BUF(p)) \ free(p); \ } while(0) /* Test harness */ int main(void); int main(void) { char *p, *p2; SASPRINTF(p, "%s", "foo"); SASPRINTF(p2, "%s", "Really long string, really."); printf("%s\n%s\n", p, p2); SASPRINTF_FREE(p); SASPRINTF_FREE(p2); exit(EXIT_SUCCESS); } I was going to say "...but you have to be pretty insane to do this", but I haven't managed to get incorrect-but-compiling code out of the above macros. Of course, I'm not at all convinced that it's faster than asprintf... (even after the obvious optimizations.)