Function Pointer from base class

Question

i need a Function Pointer from a base class. Here is the code:

class CActionObjectBase
{
  ...
  void AddResultStateErrorMessage( const char* pcMessage , ULONG iResultStateCode);
  ...
}

CActionObjectCalibration( ): CActionObjectBase()
{
 ...
 m_Calibration = new CCalibration(&CActionObjectBase::AddResultStateErrorMessage); 
}

class CCalibration
{
 ...
 CCalibration(void (CActionObjectBase::* AddErrorMessage)(const char*, ULONG ));
 ...
 void (CActionObjectBase::* m_AddErrorMessage)(const char*, ULONG );
}

Inside CCalibration in a Function occurs the Error. I try to call the Function Pointer like this:

if(m_AddErrorMessage)
{
 ...
 m_AddErrorMessage("bla bla", RSC_FILE_ERROR);
}

The Problem is, that I cannot compile. The Error Message says something like: error C2064: Expression is no Function, that takes two Arguments.

What is wrong?

regards camelord

Lara Bailey · Accepted Answer · 2010-03-22 10:40:33Z

2

You need to provide an object on which you call the member function:

CActionObjectBase* pActionObjectBase /* = get pointer from somewhere */ ;

(pActionObjectBase->*m_AddErrorMessage)("bla bla", RSC_FILE_ERROR);

Unlike normal object and function pointers, pointers to members can only be deferenced using an object of the appropriate type via the .* (for objects and references) or ->* (for pointers to objects) operators.

edited Mar 22, 2010 at 10:40

answered Mar 22, 2010 at 10:34

Lara Bailey

802k110 gold badges650 silver badges667 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Andreas Brinck · Accepted Answer · 2010-03-22 10:40:37Z

0

You need to invoke m_AddErrorMessage on an object, something like:

(something->*m_AddErrorMessage)(...)

edited Mar 22, 2010 at 10:40

answered Mar 22, 2010 at 10:32

Andreas Brinck

52.9k15 gold badges87 silver badges114 bronze badges

8 Comments

Lara Bailey Over a year ago

If he's using m_AddErrorMessage unqualified then this is probably a CCalibration which isn't a CActionObjectBase. edit: you've fixed ->* / ->

Andreas Brinck Over a year ago

@Charles You're right, I changed this-> to something-> instead.

camelord Over a year ago

Do i really need to pass an Object of CActionObjectBase to CCalibration? I tried to avoid this by using a Function Pointer as Parameter. Then i can call the CCalibration Function with an Object, derived from CActionObjectBase, calling the Function like i tried to show above: m_Calibration = new CCalibration(&CActionObjectBase::AddResultStateErrorMessage);

Lara Bailey Over a year ago

It's not a function pointer, it's a pointer to a member and you can't call a member function (whether via a pointer to member or directly) without having an object to call it on. So yes, you do need an object to call the function on.

Andreas Brinck Over a year ago

@Camelord As both me and Charles have stated you need an object to call the member function pointer on, the pointer to AddResultStateErrorMessage is the same for all instances of CActionObjectBase.

|

Collectives™ on Stack Overflow

Function Pointer from base class

2 Answers 2

Comments

8 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

8 Comments

Your Answer

Sign up or log in

Post as a guest

Related