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Join Date: Nov 2007

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abhishek2301 abhishek2301 is offline

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Require help to solve!!!

May 28th, 2009

Hello,
I require a help on a basic issue.
I have 2 classes and I want to have an interaction among the classes.
Suppose my 2 classes are testA and testB. Now I want a handle of object pointer in each class to the other class. Like I want a variable in testA to be testB* t and a variable in testB to be testA* t.
How can I implement this situation???
I have included the code for easy understanding. This code doesn't work since it is not able to resolve the declarations.
Your help is highly appreciated!!!

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <stdio.h>
 
class TestA {
  public:
    TestA();
    int id; 
    TestB* b;
    void testPrint();
    void test();
    void set(TestB* t);
};
 
void TestA::testPrint() {
  printf("I am in class TestA\n");
}
 
TestA::TestA() {
  id = 1;
}
 
void TestA::set(TestB* t) {
  b = t;
}
 
void TestB::test() {
  printf("My ID is: %d and the other ID is: %d\n", this->id, b->id);
}
 
class TestB {
  public:
    TestB();
    TestA* a;
    int id;
    void testPrint();
    void test();
    void set(TestA* t);
};
 
void TestB::testPrint() {
  printf("I am in class TestB\n");
}
 
TestB::TestB() {
  id = 2;
}
 
void TestB::set(TestA* t) {
  a = t;
}
 
void TestB::test() {
  printf("My ID is: %d and the other ID is: %d\n", this->id, a->id);
}
#include <stdio.h>

class TestA {
  public:
    TestA();
    int id; 
    TestB* b;
    void testPrint();
    void test();
    void set(TestB* t);
};

void TestA::testPrint() {
  printf("I am in class TestA\n");
}

TestA::TestA() {
  id = 1;
}

void TestA::set(TestB* t) {
  b = t;
}

void TestB::test() {
  printf("My ID is: %d and the other ID is: %d\n", this->id, b->id);
}

class TestB {
  public:
    TestB();
    TestA* a;
    int id;
    void testPrint();
    void test();
    void set(TestA* t);
};

void TestB::testPrint() {
  printf("I am in class TestB\n");
}

TestB::TestB() {
  id = 2;
}

void TestB::set(TestA* t) {
  a = t;
}

void TestB::test() {
  printf("My ID is: %d and the other ID is: %d\n", this->id, a->id);
}

Last edited by abhishek2301; May 28th, 2009 at 12:21 pm. Reason: wrong code tags

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Join Date: Dec 2005

Posts: 5,850

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Salem

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Void main'ers are DOOMed

Re: Require help to solve!!!

May 28th, 2009

Right before class TestA put this line

class TestB;

Last edited by Salem; May 28th, 2009 at 1:12 pm.

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Join Date: Nov 2007

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abhishek2301 abhishek2301 is offline

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Re: Require help to solve!!!

May 28th, 2009

I don't think it will solve the problem.
Check the output:
testA.C:26: error: invalid use of undefined type ‘struct TestB’
testA.C:3: error: forward declaration of ‘struct TestB’
testA.C: In member function ‘void TestB::test()’:
testA.C:27: error: invalid use of undefined type ‘struct TestB’
testA.C:3: error: forward declaration of ‘struct TestB’
testA.C:27: error: ‘b’ was not declared in this scope

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Join Date: Dec 2005

Posts: 5,850

Reputation: Salem has a reputation beyond repute

Solved Threads: 749

Salem

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Void main'ers are DOOMed

Re: Require help to solve!!!

May 28th, 2009

Well it won't because it doesn't know what TestB is yet.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
class TestB;
class TestA {
  // stuff
};
class TestB {
  // stuff
};
// methods
class TestB;
class TestA {
  // stuff
};
class TestB {
  // stuff
};
// methods

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Join Date: Nov 2007

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Reputation: abhishek2301 is an unknown quantity at this point

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abhishek2301 abhishek2301 is offline

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Re: Require help to solve!!!

May 28th, 2009

Thanks very much!!!
I need a little more help.
If I want to place testA.C and testB.C in separate files then how to do it???
Like the following:
testA.C should look like:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include "testB.C"
class testA {
// stuff
};
#include "testB.C"
class testA {
// stuff
};

testB.C should look like:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include "testA.C"
class testB {
// stuff
};
#include "testA.C"
class testB {
// stuff
};

But the above method gives error for multiple declarations.
How to fix this issue???

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Join Date: Dec 2005

Posts: 5,850

Reputation: Salem has a reputation beyond repute

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Salem

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Void main'ers are DOOMed

Re: Require help to solve!!!

May 28th, 2009

Well the classes themselves go in
TestA.h and TestB.h

The actual implementations go in
TestA.cpp and TestB.cpp

Further, when you do something like
b->id
within an 'A' member function, you should really use something like
b->getID()
so that later on, when you make all the data private, your code will still work.

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Join Date: Nov 2007

Posts: 19

Reputation: abhishek2301 is an unknown quantity at this point

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abhishek2301 abhishek2301 is offline

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Re: Require help to solve!!!

May 28th, 2009

Well,
My files are like this:
testA.h

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <stdio.h>
#include "testB.h"
 
class TestA {
  public:
    TestA();
    int id; 
    TestB* b;
    void testPrint();
    void test();
    void set(TestB* t);
};
#include <stdio.h>
#include "testB.h"

class TestA {
  public:
    TestA();
    int id; 
    TestB* b;
    void testPrint();
    void test();
    void set(TestB* t);
};

testA.C

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include "testA.h"
 
void TestA::testPrint() {
  printf("I am in class TestA\n");
}
 
TestA::TestA() {
  id = 1;
}
 
void TestA::set(TestB* t) {
  b = t;
}
 
void TestA::test() {
  printf("My ID is: %d and the other ID is: %d\n", this->id, b->id);
}
#include "testA.h"

void TestA::testPrint() {
  printf("I am in class TestA\n");
}

TestA::TestA() {
  id = 1;
}

void TestA::set(TestB* t) {
  b = t;
}

void TestA::test() {
  printf("My ID is: %d and the other ID is: %d\n", this->id, b->id);
}

testB.h

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <stdio.h>
#include "testA.h"
 
class TestB {
  public:
    TestB();
    TestA* a;
    int id;
    void testPrint();
    void test();
    void set(TestA* t);
};
#include <stdio.h>
#include "testA.h"

class TestB {
  public:
    TestB();
    TestA* a;
    int id;
    void testPrint();
    void test();
    void set(TestA* t);
};

testB.C

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 C++ Syntax (Toggle Plain Text) 
#include "testB.C"
 
void TestB::testPrint() {
  printf("I am in class TestB\n");
}
 
TestB::TestB() {
  id = 2;
}
 
void TestB::set(TestA* t) {
  a = t;
}
 
void TestB::test() {
  printf("My ID is: %d and the other ID is: %d\n", this->id, a->id);
}
#include "testB.C"

void TestB::testPrint() {
  printf("I am in class TestB\n");
}

TestB::TestB() {
  id = 2;
}

void TestB::set(TestA* t) {
  a = t;
}

void TestB::test() {
  printf("My ID is: %d and the other ID is: %d\n", this->id, a->id);
}

On compiling
g++ -c testA.C or g++ -c testB.C
giving many multiple declaration errors!!!
Please help me to fix this issue!!!

•

Join Date: Dec 2005

Posts: 5,850

Reputation: Salem has a reputation beyond repute

Solved Threads: 749

Salem

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Void main'ers are DOOMed

Re: Require help to solve!!!

May 28th, 2009

You didn't follow my replies.

ONE of your header files needs the class forward declaration.
AND both of them should NOT include the other.

In my original example, TestB.h could include TestA.h, but not vice-versa.

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Join Date: Nov 2007

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Reputation: abhishek2301 is an unknown quantity at this point

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abhishek2301 abhishek2301 is offline

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Re: Require help to solve!!!

May 28th, 2009

Thanks a lot!!!
I think I am not considering dependencies.
OK..Now I am able to compile testA.C
But then how to compile testB.C
g++ -c testB.C gives error now!!!

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Join Date: Sep 2008

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mostermand mostermand is offline

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Re: Require help to solve!!!

#10

May 29th, 2009

put the declaration in the header file and the definition in the other

 Help with Code Tags 
 CPP Syntax (Toggle Plain Text) 
//declaration
class foo
{
    void bar();
};
 
//definition
void foo::bar()
{
}
//declaration
class foo
{
    void bar();
};

//definition
void foo::bar()
{
}