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C++ pointer to member function: How?

Started by HimitsuMonban Jan 4, 2002 at 10:57 PM 1 replies 550+ views

Original Post

Jan 4, 2002 at 10:57 PM

Hey there, can anyone help me figure out why this won't work?:

  #include <iostream.h>

class myClass
{
public:
	myClass(void)
	{
		think = myFunction;
	}
	void (*think)(void);
	void myFunction (void)
	{
		cout << "Hello" << endl;
	}
};

void main (void)
{
	myClass object;
	object.think();
}

When compiling in Microsoft Visual C++ 6.0 I get the following error message: c:\cstuff\ptofunction\pointer.cpp(8) : error C2440: '=' : cannot convert from 'void (__thiscall myClass::*)(void)' to 'void (__cdecl *)(void)' There is no context in which this conversion is possible Thanks in advance! ========================= "The staff in the hand of a wizard may be more than a prop for age," -Hamá the doorward from 'Lord of the Rings' by J. R. R. Tolkien Edited by - HimitsuMonban on January 5, 2002 3:05:59 AM

HimitsuMonban

Author

HimitsuMonban

Jan 5, 2002 at 2:18 AM

I have found out through a lot of trial-and-error that the following code works:

  #include <iostream.h>

class myClass
{
public:
	void myFunction(void)
	{
		cout << "Hello" << endl;
	}
};

typedef void (myClass::*pmFunction)(void);

pmFunction pMyFunction = &myClass::myFunction;

void main()
{
	myClass object;
	myClass* pObject = &object

	(pObject->*pMyFunction)();
}

But this still does not solve my problem of being able to have the pointer inside the class itself. Cany anyone please help me rewrite this so that I can have a pointer as a member of a class which can point to a member function of that class? Thanks in advance!

=========================
"The staff in the hand of a wizard may be more than a prop for age," -Hamá the doorward from ''''Lord of the Rings'''' by J. R. R. Tolkien

twanvl

Jan 5, 2002 at 7:10 AM

In your first code:

void (*think)(void)
is a pointer to a __cdecl function (as all functions outside classes), while
void myFunction (void)
is a __thiscall function, that means that when the code is called the function is also givin a pointer to the "this" object, which is the instance of class. The compiler automaticly sets __thiscall for functions in classes

you should declare the fuction pointer as:


void (__thiscall myClass::*think)(void)

This is a pointer that points to a function that is a member of the myClass class.
I am not 100% sure this will work, but it probably will.

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