Re: ambiguous overload

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Mon, 7 Jan 2008 11:51:58 -0500

Message-ID:

<fltlbe$ch2$1@news.datemas.de>

siddhu wrote:

On Jan 7, 8:35 am, asterisc <Rares....@ni.com> wrote:

On Jan 7, 7:43 am, onkar <onkar....@gmail.com> wrote:

#include<iostream>
using namespace std;
class Integer{
int i;
public:
Integer(int ii):i(ii){}
const Integer operator+(const Integer& rv){
cout<<"1-operator+"<<endl;
return Integer(i+rv.i);
}
Integer operator+=(Integer rv){
i+=rv.i;
cout<<"2-operator+="<<endl;
return *this;
}
friend Integer& operator+(Integer,Integer);

void display(){
cout<<"3-display()// i="<<i<<endl;
}};

Integer& operator+(Integer rv,Integer rs ){
cout<<"2-operator+="<<endl;
rv.i+=rs.i;
return rv;}

int main(void){
cout<<"buit-in types"<<endl;
int i=1,j=2,k=3;
k+=i+j;
cout<<"user defined types:"<<endl;
Integer ii(1),jj(2),kk(3);
kk+=ii+jj;
Integer d(1),b(2);
d=2+b;
d.display();
return 0;

}

g++ -g -Wall -o test test.cpp
test.cpp: In function 'Integer& operator+(Integer, Integer)':
test.cpp:22: warning: reference to local variable 'rv' returned
test.cpp: In function 'int main()':
test.cpp:33: error: ambiguous overload for 'operator+' in 'ii + jj'
test.cpp:7: note: candidates are: const Integer Integer::operator+
(const Integer&)
test.cpp:22: note: Integer& operator+(Integer,
Integer)
make: *** [test] Error 1
??

What should I do to prevent this ??

For classes like the one designed by you, often is a good idea to
overload a conversion operator like "operator int();".
That way, you don't need to overload all the needed arithmetic
operators, relational operators, ...- Hide quoted text -

- Show quoted text -

Better way to have only a friend operator+ function. Do not have
member fn. This way you can also do calcultions like
Integer I(1);
Integer J = 1 + I;

operator+ can be implemented in terms of operator+=. e.g.

friend const Integer(const Integer& I1,const Integer& I2)

Probably meant to define it as

friend const Integer operator+(const Integer ....

although I am not sure why you want it to return a 'const'.

{
    Integer temp(I1);
    temp += I2;
    return temp;
}

And the body could simply look like this

    {
        return Integer(I1.i + I2.i);
    }

There is really no need to implement it in terms of +=, is there?

V
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