gists/c-programming/asprintf.c

/*
 * asprintf.c
 *
 * Author: Intel A80486DX2-66
 * License: Creative Commons Zero 1.0 Universal
 */

#include "asprintf.h"

ssize_t asprintf(char** strp, char* format, ...) {
	va_list args;
	va_start(args, format);

	ssize_t result = (ssize_t) vsnprintf(NULL, 0, format, args);
	if (result < 0) {
		va_end(args);
		return -1;
	}

	size_t size = (size_t) result + 1;
	*strp = malloc(size * sizeof(char));
	if (*strp == NULL) {
		va_end(args);
		return -1;
	}

	result = (ssize_t) vsnprintf(*strp, size, format, args);
	va_end(args);

	if (result < 0) {
		free(*strp);
		return -1;
	}

	return result;
}

#ifdef TEST
# include <inttypes.h>
# include <math.h>
# include <stdbool.h>
# define PRINT_ASSERT(caption, test) do {                                     \
    bool test_result = (test);                                                \
    printf("[test] " caption ": %s\n", test_result ? "OK" : "failed");        \
    if (test_result == false)                                                 \
        exit(EXIT_FAILURE);                                                   \
} while (0);

int main(void) {
	const char* world = " world";

	char* output;
	size_t result = asprintf(&output, "Hello%s! -- Unsigned 32-bit type is "
		"constrained to lie\nwithin the range of integer values from "
		"%" PRIu32 " to %" PRIu32 " inclusive.", world, 0,
		(uint32_t) (powf(2.0f, 32.0f) - 1.0f));

	PRINT_ASSERT("segmentation fault", true);
	PRINT_ASSERT("no errors", errno == 0);
	PRINT_ASSERT("zero termination test", output[result] == '\0');

	printf("[asprintf (%zu)] '%s'\n", result, output);

	return 0;
}
#endif