C++ Simple Variant Boost - c++

Question

I'm attempting to create a list of objects using the variant boost.
#include <string>
#include <list>
#include <iostream>
#include <boost/variant.hpp>
using namespace std;
using namespace boost;
class CSquare;
class CRectangle {
public:
CRectangle();
};
class CSquare {
public:
CSquare();
};
int main()
{ typedef variant<CRectangle,CSquare, bool, int, string> object;
list<object> List;
List.push_back("Hello World!");
List.push_back(7);
List.push_back(true);
List.push_back(new CSquare());
List.push_back(new CRectangle ());
cout << "List Size is: " << List.size() << endl;
return 0;
}
Unfortunately, the following error is produced:
/tmp/ccxKh9lz.o: In function `main':
testing.C:(.text+0x170): undefined reference to `CSquare::CSquare()'
testing.C:(.text+0x203): undefined reference to `CRectangle::CRectangle()'
collect2: ld returned 1 exit status
I realise that everything would be fine if i used the form:
CSquare x;
CRectangle y;
List.push_back("Hello World!");
List.push_back(7);
List.push_back(true);
List.push_back(x);
List.push_back(y);
But i would like to avoid that form if at all possible, since i would like to keep my objects unnamed. This is an important requirement for my system - is there any way i can avoid using named objects?

Answer 1

Just need to change a few things and it works:
#include <iostream>
#include <list>
#include <string>
#include <boost/variant.hpp>
using namespace std;
using namespace boost;
class CRectangle
{
public:
CRectangle() {}
};
class CSquare
{
public:
CSquare() {}
};
int main()
{
typedef variant<CRectangle, CSquare, bool, int, string> object;
list<object> List;
List.push_back(string("Hello World!"));
List.push_back(7);
List.push_back(true);
List.push_back(CSquare());
List.push_back(CRectangle());
cout << "List Size is: " << List.size() << endl;
return 0;
}
Specifically, you needed to define the CRectangle and CSquare constructors (that's why you were getting a linker error) and to use CSquare() rather than new CSquare() etc. Also, "Hello World!" has type const char *, so you need to write string("Hello World!") when passing it to push_back or it will get implicitly converted to bool here (not what you want).

Answer 2

Instead of List.push_back(new CSquare()); just write
List.push_back(CSquare());
And also write defination of your constructor

Answer 3

You forget to implement the constructors CRectangle::CRectangle() and CSquare::CSquare().
Either implement them somewhere outside the class such as:
CRectangle::CRectangle()
{
// :::
};
... or implement them inside the class:
class CRectangle {
public:
CRectangle()
{
// :::
}
};
... or remove the constructor declarations altogether:
class CRectangle {
public:
};