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troubleshooting Question

re-implementing virtual assignment operator of a templated class

Avatar of jochemspek
jochemspekFlag for Netherlands asked on
C++Editors IDEs
13 Comments1 Solution459 ViewsLast Modified:
Dear all,

I have an issue with re-implementing the assignment operator of
a base class, of which the derived class is templated.

the code:

#include <string>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <exception>

using namespace std;

class AbstractProperty {
    virtual string getValue() = 0;
    virtual void setValue( string value ) = 0;
    virtual AbstractProperty & operator = ( AbstractProperty & rhs ) = 0;

template< class T >
class Property : public AbstractProperty {
    Property( T value ):
        m_value( value ){

    string getValue(){
        stringstream ss;
        ss << m_value;
        return( ss.str() );
    void setValue( string value ){
        stringstream ss;
        ss << value;
        ss >> m_value;
    AbstractProperty & operator = ( AbstractProperty & rhs ){
            Property & p = dynamic_cast<Property & >( rhs );
            this->m_value = p.m_value;
        catch( exception & e ){
            cout << "eek ! a " << e.what( ) << endl;
        return( * this );

    T m_value;

void main( void ){
    int i1 = 1;
    int i2 = 2;

    float f = 0.5;

    Property<int> Pi1( i1 );
    Property<int> Pi2( i2 );

    Property<float> Pf( f );

    Pi2.setValue( "3" );
    Pf.setValue( "0.25" );

    cout << "Pi1: " << Pi1.getValue() << endl;
    cout << "Pi2: " << Pi2.getValue() << endl;
    cout << "Pf: " << Pf.getValue() << endl;

    Pi1 = Pf; // works, but with a Bad Dynamic (as expected)
    Pi1 = Pi2; // doesn't compile, because
                //  unresolved external symbol "public: virtual class AbstractProperty
                // & __thiscall AbstractProperty::operator=(class AbstractProperty &)"

    cout << "Pi1: " << Pi1.getValue() << endl;


What I *really* don't understand, is why the two Property<int> instances
being assigned results in an unresolved function, shouldnt the two instances
compare as two Property<int> classes, and thus be implemented by the template ?
it's not a matter of the argument to the assignment operator not being constant,
Ive checked.

any input is appreciated,

Avatar of evilrix
evilrixFlag of United Kingdom of Great Britain and Northern Ireland imageSenior Software Engineer (Avast)

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