Re: operator+ in derived classes
"Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message
news:PfKdnSSPE-V-4pHbnZ2dnUVZ_v-tnZ2d@comcast.com...
Jim Langston wrote:
"Jim Langston" <tazmaster@rocketmail.com> wrote in message
news:7h_Oh.12407$1W5.11275@newsfe02.lga...
This is something someone was asking in irc. I really don't need to
do this right now, but may have to in the future. The following
code is in error (marked).
#include <iostream>
#include <string>
class Base
{
public:
Base( const int x = 0): x_( x ) {}
Base operator+( const Base b ) { Base Temp( x_ ); Temp.x_ += b.x_;
return Temp; }
int X() { return x_; }
virtual ~Base() {}
private:
int x_;
};
class Derived: public Base
{
public:
Derived( const int x = 0, const int y = 0): Base( x ), y_( y ) {}
Add here
Derived(const Base& b) : Base(b), y_(0) {}
int Y() { return y_; }
private:
int y_;
};
int main()
{
Base MyBase(10);
std::cout << MyBase.X() << "\n";
Base MyBase2 = MyBase + Base(5);
std::cout << MyBase2.X() << "\n";
Derived MyDerived( 10, 20 );
std::cout << MyDerived.X() << " " << MyDerived.Y() << "\n";
My bad, the following line is the one in error, not the one below it.
It's the operator+ that's causing the problem, not the X() and Y();
Derived MyDerived2 = MyDerived + Derived( 5, 10 );
// error C2440: 'initializing' : cannot convert from 'Base' to
'Derived' // No constructor could take the source type, or
constructor
std::cout << MyDerived.X() << " " << MyDerived.Y() << "\n";
overload resolution was ambiguous
std::string wait;
std::getline( std::cin, wait );
}
I understand the error. I am tryign to operator+ on derived, but
the only operator + is on base.
How do people handle this?
Add the constructor from Base.
That semi works. I.E. After fixing typos (actually displaying MyDerived2
values) my output is:
10
15
10 20
15 0
When I would want output of:
10
15
10 20
15 30
So I'm thinking I'm going to need to add y_ to y_ in derived. I tried to
add an operator+ to Derived with no success in getting what I want.
Derived operator+( const Derived& d ) { Derived Temp( X(), y_ ); Temp.y_ +=
d.y_; return Temp; }
Output is now
10
15
10 20
10 30
So it seems I can either add the base variables, or the derived variables,
but not both. I tried this but can't get it to compile
class Base
{
public:
Base( const int x = 0): x_( x ) {}
Base operator+( const Base b ) { Base Temp( x_ ); Temp.x_ += b.x_;
return Temp; }
int X() { return x_; }
virtual ~Base() {}
private:
int x_;
};
class Derived: public Base
{
public:
Derived( const int x = 0, const int y = 0): Base( x ), y_( y ) {}
Derived operator+( const Derived& d )
{
// Error on following line
Base TempBase = Base( this->X() ) + Base( d.X() );
// error C2662: 'Base::X' : cannot convert 'this' pointer from
'const Derived' to 'Base &'
Derived Temp( TempBase.X(), y_ );
Temp.y_ += d.y_;
return Temp;
}
int Y() { return y_; }
private:
int y_;
};
I can't figure out why I'm getting that error. It seems I can't get d.X().
I tried int TempInt = d.X() with the same error. I know outside the class
in mainline I can get a derived.X(); why cant' I in the operator+?