C / C++ / MFC

21-Feb-06 19:43

The MFC appwizard handles function pointer arrays very differently than the console appwizard. There are a variety of ways to establish a function pointer array with a console program. My favorite is:

void show1();
void show2();
void show3();
void (*pfun[3])() = { show1, show2, show3 };

This works great for a console program, but an MFC program objects saying you cannot create an array of functions, and then just to be frustrating, the error explanation says you can
create an array of pointers to functions.

I was able to create a function pointer array using typedef:
typedef void FOO();
FOO* pfun[3];
The MFC compiler compiles the above without errors, but it will not allow me to initialize the array. I get compiler errors from:

FOO* pfun[3] = { show1, show2, show3 };

and:

pfun[0] = show1;
pfun[1] = show2;
pfun[2] = show3;

and even:

pfun[0] = &show1;
pfun[1] = &show2;
pfun[2] = &show3;

How do I initialize a function pointer array that ?

CastleIsle

kakan21-Feb-06 20:12

kakan

21-Feb-06 20:12

What compiler errors do you get, exactly?

Cedric Moonen21-Feb-06 20:13

Cedric Moonen

21-Feb-06 20:13

Console and MFC application are the same for these kind of things. This is just standard C++ and this won't change if you are doing a console app or a MFC app.

Post the exact error message and the complete definition of the different functions and maybe we can help. Maybe you are trying to use class member functions which doesn't have the same prototype.

CastleIsle22-Feb-06 5:18

22-Feb-06 5:18

The following code gives me a compile error C2440
'=' : cannot convert from 'void (__cdecl MyClass::*)(void)' to 'void (__cdecl *)(void)'

Header:

class MyClass
{
MyClass();
typedef void FOO();

FOO Show;
FOO *pfun[2];
}

Source:

MyClass::MyClass()
{
pfun[0] = Show;
}

In the error message, the only difference between the two types is the scope resolution operator.

Roger Stoltz22-Feb-06 5:53

22-Feb-06 5:53

Member function pointers are a bit tricky.

The class declaration should look like this:

class CMyClass
{
public:
    void Assign()
    {
        m_FuncArray[0] = Fn1;
        m_FuncArray[1] = Fn2;
        m_FuncArray[2] = Fn3;
    }

    void Use()
    {
        // This is the tricky part
        (this->*(m_FuncArray[0]))();
    }

protected:
    // Don't forget the 'CMyClass::' in the typedef since it is member functions
    typedef void (CMyClass::*MyFuncPtr_t)();
    MyFuncPtr_t m_FuncArray[3];
    void Fn1() { TRACE( "CMyClass::Fn1 called.\n" ); }
    void Fn2() { TRACE( "CMyClass::Fn2 called.\n" ); }
    void Fn3() { TRACE( "CMyClass::Fn3 called.\n" ); }

};

It's supposed to be hard, otherwise anybody could do it!

CastleIsle22-Feb-06 10:15

22-Feb-06 10:15

Wow, this looks really promising. I am sorry I did not see your post until now. I have an out of town job commitment that will not permit me to try this out until Friday. Thank you, Roger. I can hardly wait to try it.

Roger Stoltz21-Feb-06 22:35

21-Feb-06 22:35

CastleIsle wrote:
void show1();
void show2();
void show3();
void (*pfun[3])() = { show1, show2, show3 };

There is nothing wrong with your declaration, but using a typedef for the function pointer type would make things more clear, e.g.

typedef (*MyFunctionPointer_t)();
MyFunctionPointer_t MyFunctionPointerArray[3] = { show1, show2, show3 };

There is no difference between a console app and an MFC app, it's still C/C++ synthax.

Hope this helps
--
Roger

It's supposed to be hard, otherwise anybody could do it!

CastleIsle22-Feb-06 5:04

22-Feb-06 5:04

Thank you everyone for your suggestions. This is still unresolved.

MFC app compiler should have the same c/c++ rules as the console app compiler, but it doesn't. Here is another example:

int TestArray[] = {3,4,5}; // MFC will only accept this within
// a function. MFC rejects this
// statement in a header file.
// Console compiles the line
// in either location.

Roger Stoltz22-Feb-06 5:23

22-Feb-06 5:23

CastleIsle wrote:
MFC app compiler should have the same c/c++ rules as the console app compiler, but it doesn't.

Oh, yes it does. Smile | :)

This is not dependant on whether you are building a console app or an MFC app.
Since you are DEFINING the variable in a header file you will get errors if that header file is included in more than one source file. The linker will complain about multiple definitions.
You can have as many DECLARATIONS as you want, but you can only DEFINE a variable in one place.
Probably in your console project you have only one definition since the header file is included in one source file only, but several in your MFC app since the AppWiz includes each header file in more than one source file by default.
Tip of the day: never define variables in header files.;)

If you write your statement at the top of one single source file then the variable will be defined only once. Declare it as extern in the header file to be able to access in from other source files.

If this doesn't clear things up for you, post again and describe how and where you declare your variable and why.

--
Roger

It's supposed to be hard, otherwise anybody could do it!

CastleIsle22-Feb-06 5:48

22-Feb-06 5:48

All my header files have the standard
#if !defined(gobbledygook)
#define gobbledygook
// definitions here
#endif
... supplied by Visual C++ wizardry to prevent double definitions. Anyway, I have also tried defining the function pointer array in the source file and the MFC compiler still objects to initialization. I wish you were right.

Roger Stoltz22-Feb-06 6:30