Sizeof() function of C

Question

#include<stdio.h>
void main()
{
int a=2;
if ((sizeof(a))>-1)
printf("a");
else
printf("b");
}

Why is the program giving output as b

When sizeof(a) = 4, which is greater than (-1)

Sizeof is **not a function**, it is an **operator**. That is one of the reasons why `if (sizeof a > -1 )` is valid syntax — joop, Sep 22 '14 at 15:21

AlexD · Answer 1 · 2014-09-22T15:29:34.137

4

sizeof returns size_t (which is implementation defined unsigned integer type).

So -1 gets converted to unsigned too. Assuming two's complement representation of negative integers, (unsigned)-1 is greater than (unsigned)4, hence the output is b.

edited Sep 22 '14 at 15:29

answered Sep 22 '14 at 15:18

AlexD

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Nitpicking: Depending on the implementation `sizeof` might lead to `unsigned long`. However the issue here is the `unsigned` vs. `signed`. – alk Sep 22 '14 at 15:20
@alk Yep, thanks! It is `size_t` in fact. Corrected. – AlexD Sep 22 '14 at 15:24

Sizeof() function of C

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