initializer list

[glennpl]

I dont follow the following code in the mydocument class
MyDocument(char *fn): Document(fn){} Whats going on with this code is it calling Document class constructor or something?
what about the empty brackets?

#include <iostream.h>

/* Abstract base class declared by framework */
class Document
{
  public:
    Document(char *fn)
    {
        strcpy(name, fn);
    }
    virtual void Open() = 0;
    virtual void Close() = 0;
    char *GetName()
    {
        return name;
    }
  private:
    char name[20];
};

/* Concrete derived class defined by client */
class MyDocument: public Document
{
  public:
    MyDocument(char *fn): Document(fn){}
    void Open()
    {
        cout << "   MyDocument: Open()" << endl;
    }
    void Close()
    {
        cout << "   MyDocument: Close()" << endl;
    }
};

/* Framework declaration */
class Application
{
  public:
    Application(): _index(0)
    {
        cout << "Application: ctor" << endl;
    }
    /* The client will call this "entry point" of the framework */
    NewDocument(char *name)
    {
        cout << "Application: NewDocument()" << endl;
        /* Framework calls the "hole" reserved for client customization */
        _docs[_index] = CreateDocument(name);
        _docs[_index++]->Open();
    }
    OpenDocument(){}
    void ReportDocs();
    /* Framework declares a "hole" for the client to customize */
    virtual Document *CreateDocument(char*) = 0;
  private:
    int _index;
    /* Framework uses Document's base class */
    Document *_docs[10];
};

void Application::ReportDocs()
{
  cout << "Application: ReportDocs()" << endl;
  for (int i = 0; i < _index; i++)
    cout << "   " << _docs[i]->GetName() << endl;
}

/* Customization of framework defined by client */
class MyApplication: public Application
{
  public:
    MyApplication()
    {
        cout << "MyApplication: ctor" << endl;
    }
    /* Client defines Framework's "hole" */
    Document *CreateDocument(char *fn)
    {
        cout << "   MyApplication: CreateDocument()" << endl;
        return new MyDocument(fn);
    }
};

int main()
{
  /* Client's customization of the Framework */
  MyApplication myApp;

  myApp.NewDocument("foo");
  myApp.NewDocument("bar");
  myApp.ReportDocs();
}

[keskiverto]

See http://www.learncpp.com/cpp-tutorial/114-constructors-and-initialization-of-derived-classes/

MyDocument inherits Document and therefore each MyDocument object contains a Document object portion that has to be initialized.

There is nothing to do in the body of the MyDocument(char*) constructor and therefore there are no statements within the braces