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>>>>> "seedy" == seedy  <seedy@ultranet.com> writes:

    seedy> When attempted to compile the following code using GNU's
    seedy> g++ (ver. 2.7.1) on HP-UX, I got the following error :

    seedy> news.cc: In function `int equal(const class abc &, const
    seedy> class abc &)': news.cc:23: no match for `operator ==(class
    seedy> abc, class abc)'


    seedy> #include <iostream.h>

    seedy> class abc { 
    seedy>    public : 
    seedy>       abc( int x ) { a = x; b = 0; } 
    seedy>       int a;
    seedy>       int b; 
    seedy>  inline int operator ==(abc x) { 
               return ((a==x.a) && (b==x.b)); 
    seedy>   } 
    seedy> };

    seedy> template < class Element> 
    seedy> inline int equal (Element const& e1, Element const& e2) { 
    seedy>           return e1 == e2;
    seedy> }

    seedy> main() { 
    seedy>    abc a1(5), a2(5);
    seedy> cout << "Return value is = " << equal(a1, a2) << endl; }

    seedy> Could any one explain why this error happens.  Please send
    seedy> your response via mail to 'seedy@trigent.com' or post it
    seedy> here.

My compiler gives the following error.

ub239:~$ g++ -Wall -o check check.cc
check.cc: In function `int equal(const class abc &, const class abc &)':
check.cc:14: non-const member function `abc::operator ==(abc)'
check.cc:24: called for const object at this point in file

Making int operator == (abc) a constant member function -> compiles and 
runs without error.
ie:
 inline int operator ==(abc x) const { 
               return ((a==x.a) && (b==x.b)); 
        }
--
Peter Rye   prye@cyllene.uwa.edu.au,  prye@ichr.uwa.edu.au
Respiratory Research Fellow, Princess Margaret Hospital for Children
Perth, Western Australia    Ph: +61 (09) 340 8985, Fax: +61 (09) 388 2097
** Smoking areas in restaurants are like peeing areas in swimming pools. **

seedy@ultranet.com wrote:
> 
> When attempted to compile the following code using GNU's g++ (ver. 2.7.1)
> on HP-UX, I got the following error :
> 
> news.cc: In function `int equal(const class abc &, const class abc &)':
> news.cc:23: no match for `operator ==(class abc, class abc)'
> 
> #include <iostream.h>
> 
> class abc {
>     public :
>        abc( int x )
>           {
>           a = x;
>           b = 0;
>           }
>        int a;
>        int b;
>        inline int operator ==(abc x)
>            {
>               return ((a==x.a) && (b==x.b));
>            }
>     };
> 
> template < class Element>
> inline int equal (Element const& e1, Element const& e2)
> {
>   return e1 == e2;
> 
> }
> 
> main()
> {
> abc a1(5), a2(5);
> 
> cout << "Return value is = " << equal(a1, a2) << endl;
> }
> 
> Even though the 'operator ==' is overloaded in class abc, compiler is
> reporting match not found. By making the overloaded function 'operator =='
> as friend to 'class abc' I could resolve the problem, because in this case,
> this overloaded function becomes outsider function.
> 
> As far as I know, template instantiation for function 'equal will be done
> for 'class abc'(because the passed parameters are of type class abc),
> and so the corresponding member function 'operator ==' can be used for
> template variables e1 and e2.
> 
> Could any one explain why this error happens.  Please send
> your response via mail to 'seedy@trigent.com' or post it here.
> 
> Cheers,
> 
> Praveen.

You are calling with const parameters a method that
it's parameters are not const.
change your operator== to:

       inline int operator ==(const abc & x) const
           {
              return ((a==x.a) && (b==x.b));
           }

Amir


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