Why does the below expression turn out to be true, asking for C++ specifically

Question

#include <iostream>
using namespace std;

int main()
{
    if(sizeof(int)> -1)
        cout<<"ok";
    else
        cout<<"not ok";

    return 0;
}

Isn't size of int supposed to be 4, which should be greater than -1.

unsigned compared to signed ... `4 > -1` but `4u < unsigned(-1)`. — Jarod42, Sep 08 '21 at 10:23
try initializing a size_t variable to -1 and check what happens to it in a debugger — Pepijn Kramer, Sep 08 '21 at 10:25
title says "Why does it turn out to be true" which is the expected... — 463035818_is_not_an_ai, Sep 08 '21 at 10:25
[c++ vector size. why -1 is greater than zero](https://stackoverflow.com/q/16250058/995714), [Why does this if condition fail for comparison of negative and positive integers](https://stackoverflow.com/q/18247919/995714) — phuclv, Sep 08 '21 at 10:47

Bathsheba · Accepted Answer · 2021-09-08T10:29:40.747

7

Two things:

sizeof(int) can be any positive integral value. (I've worked on a system where sizeof(char), sizeof(int) and sizeof(long) were all 1 and were all 64 bit types.)
The type returned by sizeof is an unsigned type. When comparing with -1, -1 is converted to an unsigned value, with a high magnitude. Almost certainly sizeof(int) will be less than that.

edited Sep 08 '21 at 10:29

answered Sep 08 '21 at 10:25

Bathsheba

shouldnt `sizeof(int)` be at least 4 to be compliant? – 463035818_is_not_an_ai Sep 08 '21 at 10:27
2

@463035818_is_not_a_number: Nope, the range of `int` needs to be -32767 to +32767. (C++20 widens that by 1). It can be the same range as `char`, if `char` is widened. And `sizeof(char)` *must* be 1. – Bathsheba Sep 08 '21 at 10:28
The conversion comes from _"[..] if the operand that has unsigned integer type has rank greater than or equal to the rank of the type of the other operand, the operand with signed integer type shall be converted to the type of the operand with unsigned integer type."_ ([ref. 8.3 (1.5.3)](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4713.pdf)), isn't it? – Yun Sep 08 '21 at 10:36

1 Answers1