c variadic function misbehaviour

Asked Oct 18 '18 at 07:00

Active Oct 18 '18 at 07:26

Viewed 56 times

I'm compiling very simple program on Ubuntu-14 32bit:

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

void test(char *fmt, ...) {
    va_list args;
    va_start(args, fmt);

    printf(fmt, args);

    va_end(args);
}

int main(int argc, char** argv) {
    test("%u\n", 123);
    printf("%u\n", 123);
    return 0;   
}

with

gcc -c *.c
gcc -o test.bin ./*.o

While getting this output

3214954436 
123

the first number is changing every time I run test.bin

What am I missing here?

asked Oct 18 '18 at 07:00

x_arrange

`printf(fmt, args);` is the culprit, you are passing `args` instead of `va_arg(args, int)`. – vgru Oct 18 '18 at 07:02
@AnttiHaapala - And an exact one too. I have not idea how I missed that. But I would not list the second one there myself. The question isn't about that, really. – StoryTeller - Unslander Monica Oct 18 '18 at 07:22
@StoryTeller well it goes along there :D – Antti Haapala -- Слава Україні Oct 18 '18 at 07:25
But yea, perhaps not necessary – Antti Haapala -- Слава Україні Oct 18 '18 at 07:26

c variadic function misbehaviour

0 Answers0