GetProcAddress fro member function

[Paresh Chitte]

Thanks. If we look at the MSDN help for GetProcAddress it says "The GetProcAddress function retrieves the address of an exported function or variable from the specified dynamic-link library (DLL)." Hence, we cannot use GetProcAddress in this scenario. Regards, Paresh.

[Stephen Hewitt]

It is possible, just a little messy.

Steve

[Paresh Chitte]

Please let me know if you find a way. Regards, Paresh.

[Stephen Hewitt]

First you have to find the mangled name of the function you want to import. Probably the easiest way to do this is generate a linker error. For example:

class CMyClass
{
public:
void MyFunction();
};
 
void main()
{
CMyClass mc;
mc.MyFunction();
}

Since the function CMyClass::MyFunction is not defined (it is declared) the linker produces the following error message: “error LNK2001: unresolved external symbol "public: void __thiscall CMyClass::MyFunction(void)" (?MyFunction@CMyClass@@QAEXXZ)” I have underlined the mangled name. Use this name when calling GetProcAddress Assume the following typedef:

typedef void (CMyClass::*PMyFunction)();

Then our code would look like this:

FARPROC pRaw = GetProcAddress(hModule, “?MyFunction@CMyClass@@QAEXXZ”);
PMyFunction pFun;
*(FARPROC*)&pFun = p;
 
// Now call through the pointer.
CMyClass mc;
(mc.*pFun)(); // Use “->*” if you’ve got a pointer to the class.

All in all it's a bad design and should not be contemplated; the whole think stinks of hack. Use COM instead.

Steve

[Stephen Hewitt]

http://www.codeproject.com/script/comments/forums.asp?msg=2012519&forumid=1647#xx2012519xx[^]

Steve

[Paresh Chitte]

Thanks. Regards, Paresh.

[vibindia]

Or can put the following code in DLL to create object for the class MyClass in Client Application

extern "C" __declspec(dllexport) MyClass* CreateObjectofMyClass()
{
return new MyClass(); //Ctor
}

extern "C" __declspec(dllexport) MyClass* DeleteObjectofMyClass(MyClass *a)
{
delete a; //Dtor
}

VIBIN "Fool's run away,where angle's fear to tread"

[Stephen Hewitt]

This will not help as it stands. The DLL contains the class’s functions and the EXE (what loads the DLL and wants to call into it) will contain the class definition only (no function definitions). You still need the addresses of the functions of the class in the DLL; you’ve only got the address of the class itself. You can get around this by using virtual functions however.

Steve

[Paresh Chitte]

Please refer this[^]. Please also have a look at this[^]. Regards, Paresh.

[twhall]

This works for me in Visual Studio 2008 / C++ for a static member function of a class, if there's only one class in the DLL: * Define the class .h and .cpp files in the usual way. __declspec(dllexport) seems neither necessary nor helpful. For example:

class MyClass
{
public:
static int func (int argc, char * argv []);
};

* Create a .def file for the DLL project: Project | Add New Item... | Module-Definition File (.def) * In the .def file, export the name(s) of the static member function(s) that you want to find through GetProcAddress(). For example:

LIBRARY "DLLProjectName"
EXPORTS func

* Note that the .def file doesn't declare any MyClass:: scope. I get linker "undefined symbol" errors if I try to include the class scope. I get linker ambiguity errors if there are multiple definitions of func in the library, even if they're at different class or namespace scopes. * Set the project properties to use the .def file: Project | Properties | Linker | Input | Module Definition File * In the program that will use this library, load the DLL with LoadLibrary(). Note that the DLL file name needs to be passed as a wchar_t* (not just char*). * Get the function pointer with GetProcAddress with the un-scoped name you put in the .def file:

HINSTANCE lib = LoadLibrary (...);
typedef int (* FuncT) (int, char * []);
FuncT func = FuncT (GetProcAddress (lib, "func"));
func (argc, argv);

* I don't know why this works without a class scope on func, or why it fails if I try to include the scope. * The .def file seems to handle the C++ name decoration issues; it's not necessary to know the decorated name. * I couldn't get this to work with only __declspec(dllexport) and no .def file. * With the .def file, __declspec(dllexport) doesn't seem to make any difference. * I haven't yet tried to create an instance of the class and invoke it's non-static functions from the loading program (outside of the DLL itself). I guess that's next on the agenda. Maybe I'll need to __declspec(dllexport) the class for that ...