#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>

__attribute__((format(printf, 1, 0)))
static char* strdup_printf(const char* fmt, va_list ap)
{
    char* str = NULL;
    int required_size = 0;
    va_list ap_copy;

    // find out required size
    va_copy(ap_copy, ap);
    required_size = vsnprintf(NULL, 0, fmt, ap) + 1; // add 1 for \0
    va_end(ap);
    if (required_size > 0)
        str = (char*)malloc((size_t)required_size);
    // write to str
    if (str != NULL)
    {
        va_copy(ap_copy, ap);
        vsnprintf(str, (size_t)required_size, fmt, ap);
        va_end(ap);
    }
    return str;
}

__attribute__((format(printf, 1, 2)))
char* w_strdup_printf(const char* fmt, ...)
{
    va_list ap;
    char* msg;
    va_start(ap, fmt);
    msg = strdup_printf(fmt, ap);
    va_end(ap);
    return msg;
}

int main()
{
    //printf("=== FIRST\n");
    char* a = w_strdup_printf("generror %s %d", "abcd", 70);
    printf("a %p\n", a);
    free(a);
    //printf("=== SECOND\n");
    char* b = w_strdup_printf("generro %s %d", "zabcd", 70);
    printf("b %p\n", b);
    free(b);
    return 0;
}