how to make gcc warn about arithmetic signed overflow

[James K. Lowden]

On Sat, 21 Sep 2013 19:30:02 +0100
Jonathan Wakely <jwakely.gcc@gmail.com> wrote:

> > its value can be changed using pointers
> 
> No, that's not true. You can't change the value of a const object in a
> valid program.

I don't know if we're talking C or C++ at this point, but const_cast
will surely let you change the value of a const object without treading
into undefined behavior.  

Regarding the OP's query

> > int r = ab * bc;

although the provided example is simple enough, it's the compiler's
job is to generate object code, not to do static analysis.  

Even if the values are const, in the general case they could be
modified by another module or another thread.  The compiler simply
doesn't have enough information to warn of every runtime overflow.  

--jkl