Function returning two things seperated by a comma in C

Question

Okay, so here is the code.

#include <stdio.h>
int addmult (int,int);
int main (void)
{
    int i=3,j=4,k,l;
    k = addmult(i,j);
    l = addmult(i,j);
    printf("%d %d\n",k,l);
    return 0;
}

int addmult ( int ii, int jj )
{
    int kk,ll;
    kk = ii + jj;
    ll = ii*jj;
    return(kk,ll);
}

How is it that a function is returning two things simultaneously in C?

Edit: This code is perfectly working. I wish to know, why is it working?

return a structure or an array(dynamically allocated) instead. — Grijesh Chauhan, Jul 12 '14 at 12:24
It isn't returning two things, it is just returning one thing: `ll`. — Vaughn Cato, Jul 12 '14 at 12:26
But then why is it working this way? How a function is able to return two values at a time? — user3797829, Jul 12 '14 at 12:26
It is not returning multiple values. Note the comma(',') operator in the return statement which is evaluated from left to right and returns the rightmost expression as the result. Due to which 12 is getting returned. — pankaj, Jul 12 '14 at 12:26
It does *not* return two values. The comma operator evaluates both the values `kk` and `ll` and returns only (last) `ll`. — P.P, Jul 12 '14 at 12:27

score 2 · Answer 1 · answered Jul 12 '14 at 12:27

2

Are you asking what the line

return(kk,ll);

does or how you might return multiple values from a function?

To answer the first, this code is functionally equivalent to:

int ret = (kk,ll);
return ret;

Which might make it a little clearer. This is an instance of the comma operator, which evaluates to its second operand, so the code is in fact also functionally equivalent to:

return ll;

The kk value is never used.

To address the second possible interpretation of your question: use a struct, such as:

struct product_and_sum
{
  int product;
  int sum;
};

Change the function to return a struct product_and_sum and return a suitably initialised struct value.

answered Jul 12 '14 at 12:27

pmdj

22,018
3
52
103

I got this. :) And I had one more doubt. If a function returns a value, then is it necessary to collect its value when it returns? – user3797829 Jul 12 '14 at 12:29
@user3797829 No that is optional for an example you don't collect returned value by `printf` function! ...additionally learn difference between `ret = (kk,ll);` and `ret = kk, ll;` – Grijesh Chauhan Jul 12 '14 at 12:31
1

Well, what is the difference if you can brief me a bit here? And also, not collecting the value is good enough for a user defined function as well, right? – user3797829 Jul 12 '14 at 12:32
@user3797829: It's not necessary e.g. you have instruction like `foo();`. However if you want to explicitely say that result is discarded, then you might provide void cast, e.g. `(void) foo();`. It does not have any effect on compiler, only for some static analysis tools like `splint` IIRC. – Grzegorz Szpetkowski Jul 12 '14 at 12:35
I am trying to know, is collecting the value of a function that will return a value, for example: `int foo( int a )` necessary or we can skip it as well? – user3797829 Jul 12 '14 at 12:37
1

@user3797829: lots and lots of functions return values. `sprintf`, for example, returns "the number of characters written to the output string". The question is: what would you *use* the return value for? For `sprintf`, you can use the return value or ignore it. Not using the return value of `sqrt` would be weird. – Jongware Jul 12 '14 at 12:46

Function returning two things seperated by a comma in C

1 Answers1

Linked