why does g++ not warn about division by zero?

[Axel Freyn]

Hello Martin,

the reason is given in the manual:
  -Wno-div-by-zero
           Do not warn about compile-time integer division by zero.
           Floating point division by zero is not warned about, as 
           it can be a legitimate way of obtaining infinities and NaNs.

So you should obtain a warning with "foo(4,0)", but not with "foo(4.,0)"

Axel

On Sun, Jun 21, 2009 at 03:10:34PM +0200, Martin Ettl wrote:
> Hello,
> 
> yes, i have tried -O , -O1 , -O2, -O3 and no warning is raised by g++.
> 
> Best regards
> 
> Martin
> 
> -------- Original-Nachricht --------
> > Datum: Sun, 21 Jun 2009 08:34:50 -0400
> > Von: John Fine <johnsfine@verizon.net>
> > An: Martin Ettl <ettl.martin@gmx.de>
> > CC: gcc-help@gcc.gnu.org
> > Betreff: Re: why does g++ not warn about division by zero?
> 
> > Have you tried that at various optimization levels?
> > 
> > At lower optimization levels, the "inline" keyword should not cause the 
> > function to actually get inlined.
> > 
> > If the function is not actually inlined, gcc cannot be aware of the 
> > divide by zero.
> > 
> > I don't happen to know whether gcc would warn if it were aware of the 
> > divide by zero, nor if actually inlining is sufficient to make it 
> > aware.  I'm just saying actually inlining should be necessary to make it 
> > aware of the divide by zero.
> > 
> > Martin Ettl wrote:
> > > template <typename T1, typename T2> inline T1 foo (T1 const& a, T2
> > const& b)
> > > {
> > > 	// ....
> > >     return a/b;
> > > }
> > >
> > > int main()
> > > {
> > > 	std::cout << foo(4.,0) << std::endl; 
> > > 	return 0;  
> > > }
> > >
> > > I compiled the testprogramm with following command:
> > > g++ -W -Wall -pedantic -o test test.cpp
> > >   
> 
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