Question

consider a fun.cpp file :

class fun

{

  public:

  void sum();

  void dispaly();

};


Class fun2

{

    public: 

     void subtract();


};

Now consider another c++ file execute.cpp where i want to access only subtract method of fun.cpp file..

i dont want to include “fun.cpp” file into my execute.cpp as it will increase the size(in larger projects)..

so, how can i access any particular method wihtod including the file????

Answer 1

You need to include the header file which defines the class fun(and has the declaration of subtract()) in the cpp file where you want to use the function subtract().
Note that the function must be defined though.

fun2.h

#ifndef FUN2_H
#define FUN2_H

Class fun2  
{      
    public:        
       void subtract();   
};

#endif // FUN2_H

fun2.cpp

#include "fun2.h"
void func2::subtract()
{

}

execute.cpp

#include "fun2.h"

//use subtract() through object of `fun2`

Note that, to use a member function in a particular source file, the definition of the class which declares that function should be visible to the compiler, the actual job of linking to the particular definition is done at the linking stage and as long as you follow the above format the linker shall link the appropriate function for you.