sizeof in c program output

Question

Problem Statement:-

What would be the output for the following program?

main( ) 
{ 
 printf ( "\n%d%d", sizeof ( '3' ), sizeof ( "3" ), sizeof ( 3 ) ) ; 
}

I am working with 32 bit gcc compiler. And it is printing the output as-

4, 2, 4

I am confused why it is printing 4 for sizeof ( '3' ). 3 is in single inverted commas so it will be a character right? Then it shouldn't print out 4? Am I right?

-1. There are only two `%d`'s and no commas in that `printf` string, so that is not the output. Please don't paraphrase results. — Potatoswatter, Jun 04 '13 at 04:37
You are missing one `%d` in `printf` it should be `printf("%d%d%d",...)` — Navnath Godse, Jun 04 '13 at 04:38
@Potatoswatter, I think by "single inverted comma", the OP means "apostrophe" or "single quote". Something tells me english isn't his/her first language. — Carl Norum, Jun 04 '13 at 04:38
@CarlNorum No, I mean in the format string. Look carefully at the program and look at the output. — Potatoswatter, Jun 04 '13 at 04:39
Oh gotcha. Yeah, the "smart quotes" on the character literal are another giveaway. — Carl Norum, Jun 04 '13 at 04:40
I fixed the sloppy quotes for single quotes...but I'm not fixing what should be three occurrences of `%zu` with commas and spaces separating them. — Jonathan Leffler, Jun 04 '13 at 04:42
Note that in C++, `sizeof('3')` would be 1, not 4. And if you had a machine with 16-bit `int`, it would 2, not 4, in C (but still 1 in C++). — Jonathan Leffler, Jun 04 '13 at 04:43

Carl Norum · Accepted Answer · 2013-06-04T04:42:46.470

4

Character literals are integers in C. That means sizeof('3') is the same as sizeof(int). On your machine, that looks like 4.

Editorial notes:

Don't use %d as the format string when printing sizeof results. sizeof returns a size_t, so you should use %zu instead.
You should use a correct prototype for main. That is: int main(void) or int main(int argc, char **argv). Not just main().
If you use the correct prototype for main, make sure your program returns something. return 0; at the end, for example.

edited Jun 04 '13 at 04:42

answered Jun 04 '13 at 04:35

Carl Norum

219,201
40
422
469

1

whats this "3" considered? why size 2 ? – Dineshkumar Jun 04 '13 at 04:37
`"3"` is a string literal. It contains two characters - a `'3'` and a terminating `'\0'` (null) character. – Carl Norum Jun 04 '13 at 04:39
even null 'll be added for sizeof ("\0") [it gives 2]? – Dineshkumar Jun 04 '13 at 04:41
Yes, that's a string literal that contains two `'\0'` characters. A string literal isn't necessarily a string, as you've found. – Carl Norum Jun 04 '13 at 04:43
how sizeof works? (calculates size [here it includes "\0"]) [sizeof computes results at compile time] but i don't get it.? – Dineshkumar Jun 04 '13 at 04:48
I'm not sure I understand your question. `sizeof` can compute results at runtime, too (for VLAs, for example). – Carl Norum Jun 04 '13 at 04:48

sizeof in c program output

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