Re: integer abs() overflow

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++

Date:

Sun, 05 Jul 2009 16:37:45 -0400

Message-ID:

<35adnbIRMbKEkszXnZ2dnUVZ_tOdnZ2d@giganews.com>

Jonathan Lee wrote:

Use std::abs.

--
Pete

It exhibits the same problem (see below).

No, the code that uses it exhibits the same problem. <g>

It seems

that std::abs returns a signed value, not unsigned.

Yes, that's what it's required to do.

I'm using a 32-bit Intel CPU with G++ 4.3.2

--Jonathan

// Example ----------------------------------------
#include <cstdlib>
#include <iostream>
#include <limits>

using ::std::cout;
using ::std::endl;

int main() {
    int x = std::numeric_limits<int>::min();
    cout << std::abs(x) << endl;
    cout << std::abs(x + 1) << endl;
}

// Output ----------------------------------------
-2147483648
2147483647

If the returned value is negative then the result wasn't representable
as a non-negative value. The point, though, is that this is managed for
you by the standard library, so you don't have to deal with the details
of your particular implementation's representation.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of
"The Standard C++ Library Extensions: a Tutorial and Reference"
(www.petebecker.com/tr1book)