What does sizeof(int) return in this case?

Question

#include<stdio.h>
#include<conio.h>

void main()
{   
    if(sizeof(int)>=-2)    
        printf("True");
    else
        printf("False");
}

When I am trying to compile this piece of code using Turbo C++ it is returning False instead of True . But when I tried to print the value of int the program is returning 2.

How can this be possible ? while sizeof(int) is returning 2 and yes 2>=-2 .

Why do you use TurboC++ ? It is unmaintained, and is not standard conforming.... Try [GCC](http://gcc.gnu.org/), e.g. on Linux. — Basile Starynkevitch, Oct 28 '14 at 13:02
[Integer promotion rules.](http://stackoverflow.com/questions/5563000/implicit-type-conversion-rules-in-c-operators) — jrok, Oct 28 '14 at 13:03
possible duplicate of [What is the return type of sizeof operator?](http://stackoverflow.com/questions/19870192/what-is-the-return-type-of-sizeof-operator) — eerorika, Oct 28 '14 at 13:05
Please use `int main`, `return 0` and use some `c compiler` if you intend to write C code. — Gyapti Jain, Oct 28 '14 at 13:14
@GyaptiJain `return 0` is not neccesary in `main` in C++ programs. — jrok, Oct 28 '14 at 13:20
@jrok You are right. In C++ it is not required, but just for the sake of good programming style. Moreover it appears that Abdul wants to write a C code but is using (Turbo)C++ compiler. — Gyapti Jain, Oct 29 '14 at 04:36
Trick question - (almost) everyone knows that the size of something can't be negative. — Marichyasana, Dec 09 '14 at 07:23
I remain unconvinced that `return 0` is "good style". any experienced c++ programmer is aware of this behavior — Ryan Haining, Dec 18 '14 at 08:06
possible duplicate of [Why sizeof(int) is not greater than -1?](http://stackoverflow.com/questions/24466857/why-sizeofint-is-not-greater-than-1) — phuclv, Dec 18 '14 at 08:08

Gyapti Jain · Answer 1 · 2014-10-29T04:33:38.717

16

sizeof(int) is replaced with type std::size_t which is unsigned ~~on most of the implementations~~.

Comparing signed with unsigned leads strange result because of signed being promoted to unsigned.

You can get sensible result as shown below

if(static_cast<int>(sizeof(int)) >= -2)

If you are working on a C compiler

if((int)sizeof(int) >= -2)

Compiling your code with some warning flags -Wall for example should most possibly warn about signed/unsigned comparison. (If you are not ignoring the warnings)

edited Oct 29 '14 at 04:33

answered Oct 28 '14 at 13:04

Gyapti Jain

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which any decent compiler would warn you about. – dandan78 Oct 28 '14 at 13:04
5

@dandan78: The question isn't about a decent compiler. – Mike Seymour Oct 28 '14 at 13:07
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`std::size_t` is required by the standard to be an unsigned type. – James Kanze Oct 28 '14 at 14:15
Can you please re-write the code for me so that it returns true. Thanks in advance. – Abdul Oct 28 '14 at 14:33
1

`if(1)` would be another way to get sensible results, since `sizeof` can never give a negative result – M.M Jul 16 '19 at 02:26
@M.M Actually. `if(1)` and `int main()` make sense. – Gyapti Jain Jul 18 '19 at 06:29

score 2 · Answer 2 · edited Oct 28 '14 at 21:58

2

The type of sizeof is size_t (typedef unsigned int size_t). unsigned int compared with an signed may cause wrong answer.

edited Oct 28 '14 at 21:58

Chnossos

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answered Oct 28 '14 at 13:05

wangsquirrel

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Not necessarily `unsigned int`. `unsigned long` and `unsigned long long` are probably just as frequent, if not more. The only requirement is that it be an unsigned integral type. – James Kanze Oct 28 '14 at 14:16
Can you please re-write the code for me so that it returns true. Thanks in advance. – Abdul Oct 28 '14 at 14:33
on 64-bit systems it's most probably `unsigned long` or `unsigned long long` – phuclv Dec 18 '14 at 08:29

What does sizeof(int) return in this case?

2 Answers2