Creating an Interface with an Abstract Base Class - C++ Class

C++ examples for Class:Virtual Function

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Description

Creating an Interface with an Abstract Base Class

Demo Code

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

class MyAbstractClass {

public://from   w  w w . j  a  va 2s . c om
   virtual ~MyAbstractClass() {}

   virtual void getKey(const string& header,
                       const string& key,
                             string& val) const = 0;
   virtual void exists(const string& header,
                       const string& key,
                             string& val) const = 0;
};

class MyConfigFile : public MyAbstractClass {
public:
            MyConfigFile() : in_(NULL) {}
            MyConfigFile(istream& in) : in_(&in) {}
   virtual ~MyConfigFile() {}
   virtual void getKey(const string& header,
                       const string& key,
                             string& val) const {}
   virtual void exists(const string& header,
                       const string& key,
                             string& val) const {}
protected:
   istream* in_;
};

class MyAppClass {
public:
   MyAppClass() : config_(NULL) {}
  ~MyAppClass() {}
   void setConfigObj(const MyAbstractClass* p) {config_ = p;}
   void myMethod();

private:
   const MyAbstractClass* config_;
};

void MyAppClass::myMethod() {

   string val;
   config_->getKey("Foo", "Bar", val);
   // ...
}

int main() {
   ifstream in("foo.txt");
   MyConfigFile cfg(in);

   MyAppClass m;

   m.setConfigObj(&cfg);

   m.myMethod();
}

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