difference between sizeof(foo) and sizeof(foo()) in C

Asked Jan 25 '14 at 13:04

Active Jan 25 '14 at 13:15

Viewed 107 times

What is the difference between sizeof(foo) and sizeof(foo()) where foo is any simple function. In gcc (4.7.2)
I am getting sizeof(fun) = 1 and sizeof(fun()) = 4. Earlier I perceived that foo is stored as a pointer in symbol table. Can someone explain why I am getting 1 in first case and 4 in other ?

#include<stdio.h>
int fun(){
int a=1,b=4,x=5;
printf("hi\n");
}

int main(){
printf("%d",sizeof(fun()));
}

edited Jan 25 '14 at 13:05

Grijesh Chauhan

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asked Jan 25 '14 at 13:04

Sushant Choudhary

and it doesn't actually call `fun()`. – Karoly Horvath Jan 25 '14 at 13:07
`sizeof(fun())` is easy to understand. Why is `sizeof(fun)==1`? – David Heffernan Jan 25 '14 at 13:08
that's right, I understand fun() has to be resolved as int and return 4 with sizeof , but my question was , why sizeof(fun) = 1 ? – Sushant Choudhary Jan 25 '14 at 13:10
2

The deleted answer of @GrijeshChauhan is correct. `sizeof(fun)` shouldn't compile at all. – aschepler Jan 25 '14 at 13:10
The MS compiler rejects it! A rare victory for it!! – David Heffernan Jan 25 '14 at 13:11
http://ideone.com/svhQPv ..it is giving answer 4 in case of sizeof(fun()) and compilation error in case of sizeof(fun) http://ideone.com/RRoOyj – Kamlesh Arya Jan 25 '14 at 13:12
@KamleshArya Yes, and it is obvious why that is so – David Heffernan Jan 25 '14 at 13:14
@GrijeshChauhan..thats what i am confused with. – Kamlesh Arya Jan 25 '14 at 13:15
Thanks for the answer, however, looks like gcc choose to ignore the standards , because this compiles fine with gcc. Must be to support some other thing – Sushant Choudhary Jan 25 '14 at 13:18
@SushantChoudhary Most likely it is just a bug. – David Heffernan Jan 25 '14 at 13:18
@David yes, I am also thinking the same , or may be constraint violation as the duplicate post you said is pointing to – Sushant Choudhary Jan 25 '14 at 13:22

difference between sizeof(foo) and sizeof(foo()) in C

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