C order of passing Arguments . How is this code is working?

Question

CODE

#include <stdio.h>

int main()
{

    int a =1;
    printf("%d%d%d%d\n",a,++a,++a,a);

    a=1;
    printf("%d%d%d%d\n",a,a++,++a,a);

    a=1;
    printf("%d%d%d\n",a,++a,a++);

    return 0;
}

Output

3333
3233
331

Pretty sure this is undefined behaviour - the evaluation order of arguments is unspecified. — nneonneo, Jan 06 '20 at 18:44

score 0 · Answer 1 · answered Jan 06 '20 at 18:44

0

This is "undefined behavior". You cannot rely on the order of evaluation of function arguments in C. When we say "undefined behavior" we mean that anything might happen: it might work on one compiler, it might not work on another compiler; it might work on one compiler with optimizations disabled, and not work on the same compiler with optimizations enabled; it might not work at all; it might work flawlessly; it might dump core; it might send sperm whales and bowls of petunias falling from the sky.

(See https://www.quora.com/What-is-the-passage-on-the-whale-and-the-bowl-of-petunias-about)

answered Jan 06 '20 at 18:44

Mike Nakis

56,297
11
110
142

2

And since that quora link doesn't specify, this is a reference to [Hitchhiker's Guide to the Galaxy](https://www.syfy.com/syfywire/chosen-one-of-the-day-the-falling-bowl-of-petunias-in-hitchhikers-guide-to-the-galaxy) – Code-Apprentice Jan 06 '20 at 18:50
@Code-Apprentice thank you for the far more useful link. – Mike Nakis Jan 06 '20 at 19:18
@MikeNakis why to answer the most common duplicte here\ – 0___________ Jan 06 '20 at 20:12
@P__J__ because I have always wanted to find an opportunity to mention sperm whales and bowls of petunias! – Mike Nakis Jan 06 '20 at 20:25

C order of passing Arguments . How is this code is working?

1 Answers1