CODEWITHSUNDEEP
c++templatesindirection
Yoda
Yoda

Reputation: 18068

Illegal indirection in C++ templates

I got a template class and once it gets a string as a T and the other Para* as a T. I have overloaded << for Para.

friend ostream& operator<< (ostream &wyjscie, Para const& ex){
        wyjscie << "(" << ex.wrt << ", " << ex.liczbaWystapien <<")"<< endl;
        return wyjscie;
    }

so to print it I have to use cout<<*objectOfClassPara<<endl; otherwise I will print address but I can't do it for string.

How to correct this code udner?

T t = n->key;
            //cout<<n->key<<endl;
            cout<<t<<endl;
            if (is_same<T, Para*>::value){
                cout<<*t<<endl; //IILEGAL INDIRECTION
            }

Upvotes: 1

Views: 1259

Answers (2)

Mark B
Mark B

Reputation: 96301

Your problem is that if is a runtime if check, and all possible types have to compile, regardless of whether the code could actually ever execute. So when T is string, the * causes the code to fail.

The simplest solution is to provide an overloaded operator<< that works with pointers and remove the *:

ostream& operator<< (ostream &wyjscie, Para const* ex)
{
    return wyjscie << *ex;
}

Upvotes: 2

Aesthete
Aesthete

Reputation: 18848

T t

Is not a pointer, as 0x499602D2 mentions..

T* t

Is a pointer, and can be dereferenced like cout<<*t<<endl; Template parameters need to be types, and a pointer-to-type is not valid.

Upvotes: 1

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