Re: Function pointers and Optimization flag

[John V Shahid]

I beleive you have to return the value from _f in function f(), so f
should look like this:

    int f(const int& a, const int& b) { return (this->*_f)(a,b); }

i have no idea why g++ doesn't give warning for omitting the return
statement. That's why you see in c++ a lot of main() function without
return statement although they are supposed to return int. To force a
warning use "g++ -Wall yourFile.cpp -o output", then it should gives
something similar to this:

        yourFile.cpp: In member function ‘int Calc2::f(const int&, const
        int&)’:
        yourFile.cpp:17: warning: no return statement in function
        returning non-void
        yourFile.cpp:17: warning: control reaches end of non-void
        function
        
NOTE: you still don't have to return something from main, but as a good
practice you should return the program exit status so you can use it in
a pipe or  some other chain of commands.


On Tue, 2006-10-17 at 09:30 -0700, angelo wrote:
> Hello, I am new to this group so hello to everybody.
> I start with a problem which occur when the optimization
> flag is enabled (-O1, ..., -O3) when compiling the following
> code which contain function pointers. The code compile
> with no problems and works correctly when no
> optimization is selected. When I turn-on the optimizer,
> the program produces a non-correct result. I used gcc
> 4.0.3 under Linux Ubuntu.
> Thanks in advance for any help or suggestion.
> 
> #include <iostream>
> //---------------------------------------------------------------------------
> // Calc2 use a function pointer initialized at the constructor to point
> to
> // the selected operation.
> // + No need for inheritance
> // - Indirection of pointer, hard syntax
> //---------------------------------------------------------------------------
> class Calc2 {
> public:
>     Calc2(const char op) {
>         switch(op) {
>             case '+' : _f = &Calc2::_add; break;
>             case '*' : _f = &Calc2::_mul; break;
>             case '/' : _f = &Calc2::_div; break;
>         }
>     }
>     int f(const int& a, const int& b) { (this->*_f)(a,b); }
> private:
>     int (Calc2::*_f)(const int& a, const int& b);
>     int _add(const int& a, const int& b) { return (a + b); }
>     int _mul(const int& a, const int& b) { return (a * b); }
>     int _div(const int& a, const int& b) { return (a / b); }
> };
> 
> // Main program
> int main()
> {
>     Calc2 calc2('+');
>     std::cout << calc2.f(6, 2) << std::endl;
> }
> 
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-- 
                                                          John V. Shahid