Selecting a child class problem

[danielsbrewer]

Hi,

I have an abstract class called Integrator and two child classes, EmbedRK and Rungekutta. In my main.cc what I want to do is define a variable rk as the type that I want to use (either EmbedRK and Rungekutta) depending on a config file. I have the following:

const string integrator_type = config.read<string>( "Integrator" );
cout << integrator_type << endl;
if ( integrator_type == "embedrk" )        
{                
     cout << "Integrator: Adaptive step RungeKutta" << endl;                
     const double startstep = config.read<double>( "StartStep" );                
     cout << startstep << endl;                
     EmbedRK rk(equation, startstep, tolerance);        
}        
else if ( integrator_type == "rungekutta" )        
{                
      cout << "Integrator: RungeKutta" << endl;                
      Rungekutta rk(equation, tolerance);        
}               
else        
{                
      cout << "Integrator not recognised .. exiting" << endl;                
      exit(1);        
}

The problem is that when I compile it, it complains when I use rk that 'rk' is not defined. I use it like this:

Model model_2(rk,equation);

where in this case the function is declared as follows:

Model(const Integrator &, Equations *);

Any help to sort this out would be great.

Daniel Brewer

[kuphryn]

One solution is RTTI. Pass the base case in the first parameter of model_2().

Kuphryn

[Graham]

Your problem is that you are declaring "rk" inside a block statement. That means it immediately goes out of scope at the end of that block. Your only real solution is to use a pointer:

const string integrator_type = config.read<string>( "Integrator" );
cout << integrator_type << endl;

Integrator* rk;

if ( integrator_type == "embedrk" )
{                
     cout << "Integrator: Adaptive step RungeKutta" << endl;
     const double startstep = config.read<double>( "StartStep" );
     cout << startstep << endl;
     rk = new EmbedRK(equation, startstep, tolerance);
}        
else if ( integrator_type == "rungekutta" )
{                
      cout << "Integrator: RungeKutta" << endl;
      rk = new Rungekutta(equation, tolerance);
}
else
{
      cout << "Integrator not recognised .. exiting" << endl;
      exit(1);
}

Model model2(*rk, equation);