CODEWITHSUNDEEP
c++
Periuratio
Periuratio

Reputation: 23

Invalid operands to binary expression(when using two overloaded operators at the same time)

I am receiving the following error:error: invalid operands to binary expression ('std::ostream' (aka 'basic_ostream<char>') and 'Matrix') And the related code is like:

Matrix Matrix::operator+(const Matrix &b){
    Matrix C(r,c);
    int i,j;
    if(b.r!=r||b.c!=c)
        printf("invalid operation!");
    else {for(i=0;i<r;i++)
    {
        for(j=0;j<c;j++)
        {
            C.data[i][j]=data[i][j]+b.data[i][j];
        }
        cout<<endl;
    }
    }
    return C;
}
ostream & operator<<(ostream &out, Matrix &A){
    int i,j;
    for(i=0;i<A.r;i++)
    {
        for(j=0;j<A.c;j++)
        {
            out<<setw(6)<<A.data[i][j];
        }
        cout<<endl;
    }
    return out;
}

&

    cout<<"A + B:"<<endl;
    cout << (A + B) <<endl;

But after I changed the 2nd part into this,it just went well:

    Matrix C;
    cout<<"A + B:"<<endl;
    cout << C <<endl;

I'm really confused what's wrong with the original code……actually it's part of the fixed framework of my programming homework,and I'm not allowed to change it. QAQ

Upvotes: 2

Views: 46

Answers (1)

Sam Varshavchik
Sam Varshavchik

Reputation: 118340

(A + B)

The result of this addition operation is a temporary value.

ostream & operator<<(ostream &out, Matrix &A){

Temporaries do not bind, or convert, to mutable references. C++ does not work this way. They only bind to const references. Just change the 2nd parameter of this operator<< overload to const Matrix &, and make any appropriate changes to the contents of this overload, as needed (it may be necessary to change Matrix's mysterious "data" member's operator[] overload as well, since it now gets invoked on a const class instance).

Upvotes: 1

Related Questions