c language if statement with sizeof [duplicate]

Question

#include <stdio.h>
main()
{
   if (sizeof(int) > -1)
       printf("True");
   else
       printf("False");
}

ANSWER:

False

but according to the logic sizeof(int) return 2 and if(2>-1) return 1 and it should print True.

Why it is behaving otherwise?

Answer 1

First of all, the value produced by sizeof is of size_t which is unsigned type. ^NOTE

As the unsigned type is of higher rank than the signed type, while performing the comparison, as per the norms of the relation operator, the usual arithmetic conversions are performed, meaning the signed type is promoted to unsigned type.

In your case, the -1, when considered as unsigned, represent the highest possible unsigned value, thus, no wonder

 if (sizeof(int) > -1)

Evaluates to false.

Moral of the story: Attempted comparison between a signed and an unsigned is expected to produce weird result, just as in your case. You should enable compiler warning and try to solve the issues reported by the compiler.

---

NOTE:

From C11, chapter §7.19, <stddef.h>,

size_t
which is the unsigned integer type of the result of the sizeof operator.