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May 28th, 2009

Require help to solve!!!

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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!!!

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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abhishek2301

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May 28th, 2009

Re: Require help to solve!!!

Right before class TestA put this line

class TestB;

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

Salem

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May 28th, 2009

Re: Require help to solve!!!

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

abhishek2301

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May 28th, 2009

Re: Require help to solve!!!

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

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

Salem

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May 28th, 2009

Re: Require help to solve!!!

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:

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

testB.C should look like:

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???

abhishek2301

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May 28th, 2009

Re: Require help to solve!!!

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.

Salem

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May 28th, 2009

Re: Require help to solve!!!

Well,
My files are like this:
testA.h

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

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

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

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!!!

abhishek2301

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May 28th, 2009

Re: Require help to solve!!!

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.

Salem

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May 28th, 2009

Re: Require help to solve!!!

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!!!

abhishek2301

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May 29th, 2009

Re: Require help to solve!!!

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

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

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

mostermand

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