Can you dynamically call an object from a DLL? - c++

Question

Say I have a DLL right that contains this:
//DLL
class foo {
static __declspec int Add(int a, int b)
{
return a+b
}
}
How Do I call it call the GetProc Address? I.e:
HINSTANCE hFoo = LoadLibrary("Foo.dll");
int* proc = NULL;
proc = (int*) GetProcAddress(hFoo, ??????);
//Main Exec linked to dll
How in the world would you get the address of a class created in a dll using GetProcAddress?

Answer 1

edtheprogrammerguy is right.
Here is more informations on how to get class properly exposed:
You need to prefix with the attribute :
__declspec(dllexport)...
all the features you want to expose.
See this.
Example for a C function:
__declspec(dllexport) int __cdecl Add(int a, int b)
{
return (a + b);
}
This can be simplified using MACROS: everything is explained on this helpful page.
For C++ classes, you only need to prefix each class (not every single method)
I usually do it that way :
Note : The following also ensures portability...
Include File :
// my_macros.h
//
// Stuffs required under Windoz to export classes properly
// from the shared library...
// USAGE :
// - Add "-DBUILD_LIB" to the compiler options
//
#ifdef __WIN32__
#ifdef BUILD_LIB
#define LIB_CLASS __declspec(dllexport)
#else
#define LIB_CLASS __declspec(dllimport)
#endif
#else
#define LIB_CLASS // Linux & other Unices : leave it blank !
#endif
Usage :
#include "my_macros.h"
class LIB_CLASS MyClass {
}
Then, to build, simply :
Pass the option -DBUILD_LIB to the usual compiler command line
Pass the option -shared to the usual linker command line

Answer 2

You can't get the address of a class from a .dll. If you want to use a class instance from a .dll, use dllexport/dllimport, which lets you export the class and use it as if it were declared locally.
Reference from Microsoft:
http://msdn.microsoft.com/en-us/library/81h27t8c(v=vs.80).aspx

Answer 3

I was trying to create an example of Explicit Linking Here is the example I finally came up with, I apologize for not specifically mentioning this earlier.
Here we go:
//DLL
#include "main.h"
#include <windows.h>
#include <stdexcept>
using namespace std;
class FOO{
static __declspec double ADD(double a, double b)
{
return a+b;
}
}
//EXEC
#include <windows.h>
#include <iostream>
#include <stdio.h>
using namespace std;
typedef double (*MYPROC)(double, double);
int main()
{
double d1 = 10;
double d2 = 30;
double retval;
MYPROC procx = NULL;
DWORD err;
HINSTANCE hDll = LoadLibrary("DynamicLinkTester.dll");
if(hDll != NULL)
{
cout << "Success";
procx = (MYPROC) GetProcAddress(hDll, "_ZN7MathDLL5MathX3ADDEdd");
if(NULL != procx )
{
retval= (procx)(d1, d2);
cout << retval;
}
}
}
If anyone was wondering the same thing as me:
While you can't explicitly call a class/object from a dll you can call its method.