nested calls to printf

Question

#include <stdio.h>
void main()
{
   printf("%d", printf("%d",printf("Hello world!\n")));
}

Why this gives output as 132 ? hello world is 13 units long.

Please use a proper title, don't just put the code in the title. — Barmar, Apr 13 '18 at 02:37
A proper title... "Can't understand a C Code" is too generic. — Daniele Cappuccio, Apr 13 '18 at 02:39
You're printing characters as integers. What do you expect it to print? The length of the string? — Matt, Apr 13 '18 at 02:39
@Matt actually, it does not print characters at all. It does print the return value of the `printf()` function. — Daniele Cappuccio, Apr 13 '18 at 02:42

score 4 · Accepted Answer · edited Apr 13 '18 at 06:53

4

You may be able to see what's happening more clearly if you split the statement into several statements:

int temp1 = printf("Hello world!\n");
int temp2 = printf("%d", temp1);
printf("%d", temp2);

The first printf prints Hello world!\n. Since this is 13 characters, it returns 13.

The second printf prints 13. Since this is 2 characters, it returns 2.

The third printf prints 2.

So the full output will be:

Hello world!
132

It would have been more obvious what's going on if you added more newlines:

printf("%d\n", printf("%d\n",printf("Hello world!\n")));

would print:

Hello world!
13
3

edited Apr 13 '18 at 06:53

Lundin

195,001
40
254
396

answered Apr 13 '18 at 02:40

Barmar

741,623
53
500
612

thank you, i got it. I thought it was one hundred and thirty two. – Dhruba Goswami Apr 13 '18 at 02:41
It would have been less confusing if you put spaces or newlines after the numbers. – Barmar Apr 13 '18 at 02:44
actually it's returning Hello world! 13 3 is it for the new line ? – Dhruba Goswami Apr 13 '18 at 02:55
@DhrubaGoswami Yep, you're getting the hang of it now :) I think that last 2 was just a typo here. – Lundin Apr 13 '18 at 06:52
@Lundin Not a typo, just forgot that the change would have a secondary effect, I hadn't actually tried it. – Barmar Apr 13 '18 at 15:28

score 2 · Answer 2 · answered Apr 13 '18 at 02:42

open man 3 printf and check what it returns

Upon successful return, these functions return the number of characters printed (excluding the null byte used to end output to strings).

In your case printf("Hello world!\n") 1st it prints Hello world! and then returns no of printable char which is 13 and again it prints 2 as 13 has 2 char.

nested calls to printf

2 Answers2