Pointer to a Member Function

I've need to assign a pointer to a function, which is easy enough.. but the function in question is a public member of a class. Visual Studio is giving me this error:

Code:

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error C2440: '=' : cannot convert from 'void (__thiscall CTextManager::* )(int)' to 'void (__cdecl *)(int)'

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How can I make a pointer to a member function? Or is this impossible/hackish?

[EDIT] Forgot to mention that the member function is non-static

post some code also

I wasn't sure how much it would help... But heres the function in question:

Code:

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void CTextManager::Open(SOpenParams *pParams)
{
        m_szText = "";
        pParams->Update = UpdateText;

        m_pFileManager->Open(pParams);
}

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Code:

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class CTextManager
{
public:
        CTextManager(HWND hWnd);
        ~CTextManager();

        // Text Manager Functions
        void SetFileManager(CFileManager *pFileManager) { m_pFileManager = pFileManager; }
        void Resize(RECT rect);
        void Updated();

        // File Manager Functions
        void Open(SOpenParams *pParams);
        void Save(SSaveParams *pParams, bool bSaveAs);
        void UpdateText(int iProgress);

        // Search Functions
        void Search();
private:
        HMODULE m_hRichEdit;                        // Rich edit library
        HWND m_hParent;                                        // Main window
        HWND m_hEdit;                                        // Edit Control
        CFileManager *m_pFileManager;        // File Manager
        CSearch m_Search;                                // Search Algorithm

        SSaveParams *m_pSaveParams;
        SOpenParams *m_pOpenParams;
        string m_szText;

        bool m_bUpdated;        // Flag to show whether the text has been updated since we last did something
};

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And the SOpenParams struct

Code:

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struct SOpenParams
{
        LPSTR szText;                                                                        // Buffer to store text
        void (*Opened)(bool bSuccess, SError error);        // Function to call when file has been opened
        void (*Update)(int progress);                                        // Function to call to update text
        bool bUpdated;                                                                        // True when Update() has finished
        int iChunkSize;                                                                        // Amount of chars to read in a chunk

        SOpenParams();
        ~SOpenParams();

        CRITICAL_SECTION *pcsFileMgrData;
private:
        char const *szFilePath;                        // Pointer to the buffer containing the file path

        friend class CFileManager;
        friend void __cdecl OpenThread(void *pParams);
};

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Code:

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typedef RETURN_TYPE(CLASS_NAME::*NAME)(ARGUMENT_LIST_TYPES);

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ex:

Code:

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class CStuff
{
  public:
    void Method(int Arg);
};

typedef void(CStuff::*Pointer)(int);

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I think you declare the function pointer like this:

Code:

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void (*classname::funcpointer)(args) = classname::somefunc;

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Sorry if I sound stupid, but where would I put that piece of code, dwks? I've not really handled many function pointers before :s certainly not from member functions heh.. =/

Code:

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#include <iostream>
using namespace std;

class Apple
{
public:

        double multiply(int num1, double num2)
        {
                return num1 * num2;
        }
};


int main()
{
        double (Apple::* myFuncPtr)(int, double);
        myFuncPtr = Apple::multiply;

        Apple myApple;
        double answer = (myApple.*myFuncPtr)(10, 2.33);
       
        cout<<answer<<endl;

    return 0;
}

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Quote:

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Originally Posted by dwks

I think you declare the function pointer like this:

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Except the * is in the wrong place!

Ah thanks 7stud, that clears it up, however a new problem arises... The file in which SOpenParams is in is included by the file which has the class CTextManager in it since CTextManager uses the SOpenParams struct as a member variable.. A forward declare won't work. This is tricky... This is the file linkage of my program

Code:

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                                  Error.h
                                /      \
                                /        \
        CSearch.h      CFileManager.h  Error.cpp
      /        \    /              \
      /          \  /                \
    /            \ /                  \
CSeach.cpp    CTextManager.h        CFileManager.cpp
            /                  \
            /              \
          /                \
      main.cpp        CTextManager.cpp

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SOpenParams is in CFileManager.h
CTextManager is in CTextManager.h
SOpenParams is used in the CFileManager files and CTextManager files.

This means that I cant simply include CTextManager into CFileManager :s

Quote:

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however a new problem arises.

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...and what is it?

I cant declare the pointer as

void (*CTextManager::UpdateText)(int)

because CTextManager isnt defined yet, and a forward declare doesnt work because I'm trying to access a member function.

Nevermind, I've altered my program design so that this is no longer a problem.

Quote:

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Originally Posted by Magos

ex:

Code:

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class CStuff
{
  public:
    void Method(int Arg);
};

typedef void(CStuff::*Pointer)(int);

---

---

Lemme complete this for you (this is how you would use it):

Code:

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CStuff stuff;

Pointer myFuncPtr = CStuff::Method;

stuff.myFuncPtr(5);

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Quote:

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Originally Posted by homeyg

Quote:

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Originally Posted by Magos

Code:

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class CStuff
{
  public:
    void Method(int Arg);
};

typedef void(CStuff::*Pointer)(int);

---

---

Lemme complete this for you (this is how you would use it):

Code:

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CStuff stuff;

Pointer myFuncPtr = CStuff::Method;

stuff.myFuncPtr(5);

---

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A couple of problems:

1) There is no function definition anywhere.

2) VC++6 gives me an error using this syntax:

stuff.myFuncPtr(5);

It complains that myFuncPtr is not a member of CStuff. Does that work for you? What compiler are you using?

Quote:

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Originally Posted by 7stud

A couple of problems:

1) There is no function definition anywhere.

2) VC++6 gives me an error using this syntax:

stuff.myFuncPtr(5);

It complains that myFuncPtr is not a member of CStuff. Does that work for you? What compiler are you using?

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Okay.

Code:

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Pointer myFuncPtr = CStuff::Method;

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Should be (to be 100% standard):

Code:

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Pointer myFuncPtr = &CStuff::Method;

---

Code:

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stuff.myFuncPtr(5);

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Should be:

Code:

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stuff.*myFuncPtr(5);

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(the pointer has to be dereferenced to be used)

I'm still getting an error:

Code:

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#include <iostream>

using namespace std;

class CStuff
{
    public:
        int Method(int Arg);
};

typedef int (CStuff::*Pointer)(int);

int main()
{
    Pointer myFuncPtr = &CStuff::Method;
   
    CStuff stuff;
   
    int i = stuff.*myFuncPtr(5);
    cout<<i<<endl;
   
    cin.get();
    return 0;
}

int CStuff::Method(int Arg)
{
    return Arg;
}

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The error is (using Dev-C++):

Quote:

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22 C:\Documents and Settings\John Aurandt\My Documents\Source Folder\FunctPtrTest2.cpp must use .* or ->* to call pointer-to-member function in `myFuncPtr (...)'

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I suggest that you go back and examine the format in my earlier post. The format Magos posted does not work for me either.

You should also take that long error message out of code tags and put it in quote tags so that that the screen width returns to a normal size.

Yeah if you put the parentheses around the dereferenced pointer in the call, it works.

Quote:

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Code:

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Pointer myFuncPtr = CStuff::Method;

---

Should be (to be 100% standard):

Code:

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Pointer myFuncPtr = &CStuff::Method;

---

Code:

---

stuff.myFuncPtr(5);

---

Should be:

Code:

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stuff.*myFuncPtr(5);

---

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Is that right? C supports all four.

Code:

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user@0[~]$ cat functionpointer.c
#include <stdio.h>

void func(void) {
    puts("func()");
}

int main(void) {
    void (*f1)(void) = func, (*f2)(void) = &func;

    f1();
    (*f2)();

    return 0;
}
user@0[~]$ gcc -W -Wall -ansi -pedantic -O2 -s -o functionpointer functionpointer.c
user@0[~]$ cp functionpointer.c functionpointer.cpp
user@0[~]$ g++ -W -Wall -ansi -pedantic -O2 -s -o functionpointer_cpp functionpointer.cpp
user@0[~]$

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It seems like C++ supports all forms, too . . . .

Quote:

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Originally Posted by dwks

Is that right? C supports all four.

Code:

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user@0[~]$ cat functionpointer.c
#include <stdio.h>

void func(void) {
    puts("func()");
}

int main(void) {
    void (*f1)(void) = func, (*f2)(void) = &func;

    f1();
    (*f2)();

    return 0;
}
user@0[~]$ gcc -W -Wall -ansi -pedantic -O2 -s -o functionpointer functionpointer.c
user@0[~]$ cp functionpointer.c functionpointer.cpp
user@0[~]$ g++ -W -Wall -ansi -pedantic -O2 -s -o functionpointer_cpp functionpointer.cpp
user@0[~]$

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It seems like C++ supports all forms, too . . . .

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We're talking about member functions for classes, so C is irrelevant.

have a read of the function pointer tutorials.

you might also want to have a look at boost.function.
it's much more flexible and has a nicer syntax.

which would you rather use?

Code:

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class MyClass
{
public:
    void foo(float x, char y, char z)
    { }
};

int (MyClass::*pt2Member)(float, char, char) =  &MyClass::foo;
MyClass x;
(x.*pt2Member)(1.0, 'a', 'b');

// or

MyClass x;
boost::function<void> f = boost::bind(&MyClass::foo, &x);
f(1.0, 'a', 'b');

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This does come at a small performance cost but the flexibility and readability far outweight this IMNSHO.

Quote:

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We're talking about member functions for classes, so C is irrelevant.

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You said:

Quote:

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Code:

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Pointer myFuncPtr = CStuff::Method;

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Should be (to be 100% standard):

Code:

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Pointer myFuncPtr = &CStuff::Method;

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Both work. And both are "100% standard".

Besides, C has everything to do with it. The reason C++ has two different syntaxes for the same thing is that it was inherited from C. The reason C has both methods is a long story.

In C, and C++, given func is declared as

Code:

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void (*func)(void)

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, &func is the same as func, and func() is the same as (*func)(). It's part of the language.

Quote:

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Both work. And both are "100% standard".

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I read somewhere (when searching for info on member-pointers) that leaving the & out is non-standfard, and that GCC doesn't even allow it to be missing. I don't have GCC though so I cannot confirm it.

Quote:

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and func() is the same as (*func)()

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Plain function pointers, sure. But method pointers need the (C.*M)() rather than C.M(), or the compiler (in my case MSVC2003) thinks I'm trying to call a non-existing method rather than use the pointer.

And yes the parantehses needs to be there, forgot it in my earlier post.

Quote:

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Originally Posted by dwks

In C, and C++, given func is declared as

Code:

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void (*func)(void)

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, &func is the same as func, and func() is the same as (*func)(). It's part of the language.

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true, but as has already been mentioned, we're not talking about free function pointers here, we're talking about member function pointers, which have a different syntax.

Quote:

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Originally Posted by dwks

You said:

Both work. And both are "100% standard".

Besides, C has everything to do with it. The reason C++ has two different syntaxes for the same thing is that it was inherited from C. The reason C has both methods is a long story.

In C, and C++, given func is declared as

Code:

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void (*func)(void)

---

, &func is the same as func, and func() is the same as (*func)(). It's part of the language.

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Dev-C++ won't compile when you use

Code:

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funcPtr = Blah::func;

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or

Code:

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myClass.*funcPtr(blah);

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