Re: operator+ in derived classes
"Jim Langston" <tazmaster@rocketmail.com> wrote in message
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"Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message
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Jim Langston wrote:
"Jim Langston" <tazmaster@rocketmail.com> wrote in message
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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
<Snipped trial and error til I got it right>
This is what I wound up donig. Is this the way you would necessarily do it?
#include <iostream>
#include <string>
class Base
{
public:
Base( const int x = 0): x_( x ) {}
Base operator+( const Base b ) const { Base Temp( x_ ); Temp.x_ += b.x_;
return Temp; }
int X() const { 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 ) const
{
Base TempBase = Base( this->X() ) + Base( d.X() );
Derived Temp( TempBase.X(), y_ );
Temp.y_ += d.y_;
return Temp;
}
int Y() const { 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";
Derived MyDerived2 = MyDerived + Derived( 5, 10 );
std::cout << MyDerived2.X() << " " << MyDerived2.Y() << "\n";
std::string wait;
std::getline( std::cin, wait );
}
Output is my wanted:
10
15
10 20
15 30