Question

In OOP, you want to break apart a program into multiple classes.

In C#, you would do as such:

namespace a
{
  public class ClassA
  {
     //Methods...that are defined and have code in them.

  }
}

and to use that class, you just do “using namespace a;”.

Say I want to create a class in C++, and define them, and put code in them.

class ClassA
{
  public:
   void methodA();
}

ClassA::methodA()
{
  //implementation.
}

To access this implementation, you would just use #include “ClassA.h”. I fully understand that, and then you have to implement that code again? That seems counterproductive as I like to spread my project over a lot of classes.

So what would be the proper procedure to implement ClassA and not re-implement all it’s methods again?

Answer 1

You don’t have to reimplement them in each CPP file, the C++ linker takes care of making sure the definitions get matched together.

All you need is:

A header:

#ifndef FOO_H
#define FOO_H

class Foo{
  //Junk goes here
};

#endif

A cpp:

#include "foo.h"

//implementations for junk goes here
void Foo::junk(){

}

And then you can include foo.h. Each cpp will be compiled to a .o file. Than, those .o files are handed to the linker which can figure out where definitions are and piece together the code correctly.