CODEWITHSUNDEEP
c++class
hahv
hahv

Reputation: 582

forward declared class in C++

I have a problem with C++.

I want to create two classes, A and B.

Class A has some methods that take an argument that is an instance of class B. But in Class B I also have some methods which take an argument that is an instance of class A.

I tried to forward declare class A and then define class B. Finally, I define class A.

Some code:

class A;

class B
{
  void Method1(A* instaceOfA)
 {
     instaceOfA->MethodX();
 }
  .......
};

class A
{
  Method1(B* instaceOfB);
  MethodX();
  .......
};

I code in Visual Studio 2010, and it shows an error because I invoke MethodX in class A but class A is not defined completely.

How can I solve this problem?

Upvotes: 2

Views: 176

Answers (5)

StevieG
StevieG

Reputation: 8709

Is there a reason you need to implement class B inline? If you seperate the class definitions from the implentations (ideally putting them in .h and .cpp files), this problem will go away..

//blah.h

class A;

class B
{
  void Method1(A* instaceOfA);
  .......
};

class A
{
  Method1(B* instaceOfB);
  MethodX();
  .......
}l


//blah.cpp

#include "blah.h"

class B
{
  void Method1(A* instaceOfA)
 {
     instaceOfA->MethodX();
 }
  .......
};

class A
{
  Method1(B* instaceOfB)#
  {
      instaceOfB->Method1();
  }

  MethodX();
  .......
}

Upvotes: 0

ali_bahoo
ali_bahoo

Reputation: 4863

Put the definition of B::Method1 after declaration of class A

//header file
class A;

class B
{
  void Method1(A* instaceOfA);
  .......
};

class A
{
  Method1(B* instaceOfB);
  MethodX();
  .......
};

// cpp file
 void B::Method1(A* instaceOfA);
 {
     instaceOfA->MethodX();
 }

This is the purpose of .cpp file. You declare the classes and methods in a header file then, add the definitions to the .cpp file.

Upvotes: 4

danca
danca

Reputation: 509

Is your impl code in the header file? If so, try moving it to a cpp file and #include A and B

Upvotes: 0

ghik
ghik

Reputation: 10764

I suggest moving implementations of methods outside class declarations, like this:

class A;
class B {
public:
    void Method1(A* instanceOfA);
    ...
};

class A {
public:
    void Method1(B* instanceOfB);
    void MethodX();
    ...
};

void B::Method1(A* instanceOfA) {
    ...
}

Upvotes: 1

Some programmer dude
Some programmer dude

Reputation: 409136

Define and declare the classes the other way around?

class B;

class A
{
    Method1(B* instaceOfB);
    MethodX();
};

class B
{
    void Method1(A* instaceOfA)
    {
        instaceOfA->MethodX();
    }
};

Of course, this does not work if the A::Method1 function also is inline.

Upvotes: 0

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