Using Pointers in classes of VC++

Question

4.00/5 (1 vote)

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Hi All

I have to face problem in classes by using pointers function.
for example

header file

testPtr.h

C++

class testPtr
{
    float *add(float *a,int n)
};

in main the use of this class

C++

   //testing.cpp 

// object of class
testPtr testPtrObject();

void main 
{

testPtrObject.add(a,n);

}

 
float testPtr::*add(float a int n)

{

----------
-------
}

i ve to face the problem only in case of pointer
other wise if i use simple functions in header file and then call these function by creating the objects of that class in main class i can easily access that functions and use them any whaere i neede by creating the object of that class

kindly guide me what to do in case of pointer function

Posted 29-Apr-12 21:03pm

prog786

Updated 29-Apr-12 21:05pm

Prasad_Kulkarni

v2

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3 solutions

Solution 1

I assume you have a problem calling a member function via a pointer. That is not as simple as calling a simple (non-class) function, because two things are involved: (a) the function itself (b) the object that the member function should be called on.

For your example, a member function call would look like:

typedef float* (testPtr::*MemFuncPtr) (float *a, int n);
MemFuncPtr p = &testPtr::add;

// calling sequence:
(testPtrObject.*p) (&a, n);

As you see, the syntax is awkward and one of the weaker points of C++.

Instead of handling the pointer to function and the object pointer separately, why not bundle them together into a single object. That's what is generally called a delegate.

You find a lot of good articles here on CodeProject about delegates, for example this one:

Member Function Pointers and the Fastest Possible C++ Delegates

Hope that gets you on track.

Posted 29-Apr-12 22:45pm

nv3

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Espen Harlinn · Accepted Answer · 2012-04-29T23:15:00

Solution 2

When it's declared like his:

class testPtr
{
public:
    float *add(float *a,int n);
};

The implementation should look like this:

float* testPtr::add(float* a int n)
{
//----------
//-------
}

It can then be used like this:

int main()
{
  testPtr testPtrObject;
  float b = 1.0;
  float* a =&b;
  int n = 2; 
  float* c = testPtrObject.add(a,n);

  testPtr* testPtrObjectPtr = new testPtr();
  float* c = testPtrObjectPtr->add(a,n);
  delete testPtrObjectPtr;


  }

Posted 29-Apr-12 23:15pm

Espen Harlinn

Comments

Sandeep Mewara 3-May-12 8:56am

Neat. 5ed.

Espen Harlinn 3-May-12 8:57am

Thank you, Sandeep :-D

Sergey Alexandrovich Kryukov 5-May-12 22:22pm

Good, my 5.
--SA

vaibhavbvp · Accepted Answer · 2012-04-29T23:50:00

class testPtr
{
float *add(float *a,int n)
};

inspite of creating objectthis way testPtr testPtrObject();
create object like this testPtr testPtrObject

void main
{

testPtrObject.add(a,n);

}

also here the definition that you have written is not appropriate

float testPtr::*add(float a int n)

{

----------
-------
}

change this like as float* testPtr::add(float* a, int n)