Re: floating point warnings, and gcc 4 warnings in general

["Manuel LÃpez-IbÃÃez" <lopezibanez at gmail dot com>]

Hi Scott, sorry for the late reply.

My current code gives the following warnings for your testcase (all of
them plus one bonus extra warning):

tryFloat.C:12: warning: coercion to 'float' from 'const double' may
alter its value
 int Test::getDI() const
tryFloat.C:15: warning: coercion to 'int' from 'const double' may
alter its value
 void Test::setI(const int&) int Test::getI() const short int
Test::getIS() const
tryFloat.C:19: warning: coercion to 'short int' from 'const int' may
alter its value
int main(int, char**)
tryFloat.C:31: warning: coercion to 'float' from 'double' may alter its value

You can get the patches from http://gcc.gnu.org/wiki/Wcoercion#Download

It would be great if you can test the patches or provide more
testcases or add something to the documentation (
http://gcc.gnu.org/wiki/Wcoercion ). Any feedback is welcome.

Happy coding!

Manuel.


On 13 Jul 2006 00:53:31 -0700, Ian Lance Taylor <iant@google.com> wrote:
> "Scott Lipcon" <slipcon@gmail.com> writes:
>
> >  I'm trying to figure out how to get gcc to warn on a specific problem
> > that we found in our source code.   I've attached a simple test
> > program that has a few places where floating point precision can
> > potentially be lost or cause problems.   Specifically:
> >     1)   Line 12,  returns a double as a float without an explicit
> > cast - loss of precision.  Would like a warning here.
> >     2)  Line 19,  same problem, but with fixed point - returns an int
> > as a short, without a cast - loss of precision, would like a warning
> >     3)  Line 31,  subtracts a float from a double (the constant is
> > treated as a double, the variable is explicitly cast as a float.   In
> > this particular case, as can be seen in the printf on line 34,  pi/2 -
> > pi/2 does not equal zero.   This seems like it might be harder to
> > check for, but I'd love to see a warning here as well.
>
> Manuel LÃpez-IbÃÃez is working on warnings along these lines as part
> of a Google Summer of Code project.  See
>     http://gcc.gnu.org/wiki/Wcoercion
>
> Ian