Question

I need a Function like that:

class Class_A
{
     ...
     bool ShowVariableConstituents( CString ( * ValueOutput )( double ) );
     ...
}

bool Class_A::ShowVariableConstituents( CString ( * ValueOutput )( double ) )
{
    double dUncalculatedValue;
    ....

    if( ValueOutput  )
    {
       CString strValue = ValueOutput( dUncalculatedValue );
    }
    ....
 }

Here is an example how i need to use it:

class Class_B : Class_A
{
   ...
   int Calculate();
   CString ValueOutput( double dValue );
   ...
}

CString Class_B::ValueOutput( double dValue )
{
 CString strValue;
 strValue.Format("%6.2f", ( dValue / m_dAmount * 100 ) );
 return strValue;
}

int Class_B::Calculate()
{
...
ShowVariableConstituents( & Class_B::ValueOutput );
...
}

I get the Error:

Error 1 error C2664: ‘
Class_A::ShowVariableConstituents’:
conversion of Parameter 1 from
‘CString (__thiscall Class_B::*
)(double)’ in ‘CString (__cdecl
*)(double)’ not possible

Can you help me do it right?

regards
camelord

Answer 1

To make it possible to pass pointers to member functions you should modify your function as follows:

bool ShowVariableConstituents( CString ( Class_A::* ValueOutput )( double ) )

But it will not help since you want to pass the pointer to Class_B::ValueOutput and Class_A doesn’t know anything about Class_B.

Your option is to make your function template:

template<typename UnaryOperator>
bool Class_A::ShowVariableConstituents( UnaryOperator op )
{
    double dUncalculatedValue;
    CString strValue = op( dUncalculatedValue );
    return true; // false ?
 }

Then you could use it as follows:

int Class_B::Calculate()
{
    ShowVariableConstituents( std::bind1st( std::mem_fun( &Class_B::ValueOutput ), this ) );
    return 0; // put your code here
}