snprintf_alloc

int alloc_snprintf(char** out, const char* template, ...)
{
	va_list list;
	va_start(list, template);

	int len = vsnprintf(NULL, 0, template, list);
	va_end(list);
	char* new_string = malloc((size_t)len + 1);
	assert(new_string != NULL);

	*out = new_string;
	va_start(list, template);
	len = vsnprintf(new_string, (size_t)len+1, template, list);
	va_end(list);

	return len;
}