I recently had trouble with code in proj, which used abs() from C++,
expecting it to be double instead of int. Changing to std::abs() fixed
it.
That brought up the question of what the rules are. In C, abs() is
solidly integer:
#include <stdlib.h>
int
abs(int x);
and there is fabs()
#include <math.h>
double
fabs(double x);
But C++ is different. The standard approach is <cmath> and std::abs(),
but I find claims that C++11 requires that <cmath> make (bare) abs()
overloaded, and claims that C++11 permits but does not require it.
In practice, it seems clear that the only reasonable coding approach is
to include <cmath> and then use std::abs() but the standards question
remains.
I found a test program, enhanced it, and ran it on 5 systems, with
varying results.
Is NetBSD wrong here? Or is not overloading abs() permissible?
Is Debian wrong?
----------------------------------------
/*
* This program tests if using bare abs() in C++ on a double is an
* integer or floating point abs.
*
* The Internet is conflicted over whether <cmath> MAY or SHALL provide
overloads.
*
*
https://stackoverflow.com/questions/21392627/abs-vs-stdabs-what-does-the-reference-say
* https://cplusplus.com/reference/cmath/abs/
* https://github.com/OSGeo/PROJ/pull/4486
*/
#include <iostream>
//#include <math.h>
//#include <cmath>
int main(int argc, const char * argv[])
{
double x = -1.5;
double ax = abs(x);
double sax = std::abs(x);
std::cout << "x=" << x << " ax=" << ax << " sax=" << sax << std::endl;
return 0;
}
/*
c++ -Wall cpp_abs.cpp; ./a.out
none math.h cmath both both/R
NetBSD/gcc7 1 1 1 1 1
NetBSD/gcc10 1 1 1 1 1
Debian/gcc12 1 1.5 1 1.5 1.5
macOS 10.13 DNC DNC 1.5 1.5 1.5
macOS 13 1.5 1.5 1.5 1.5 1.5
*/
