Question

I’ve been trying to create a DLL and link the DLL to my program but every time I try my program can’t find the function. The DLL loads fine but the function cant be found.

Program:

#include <iostream>
#include <windows.h>
using namespace std;

typedef void (*HelloPtr)();

int main() { 
    HelloPtr hello;
    HINSTANCE hDll = LoadLibrary("dll.dll");
    if(hDll)
    {
        hello = (HelloPtr)GetProcAddress(hDll, "hello");
        if(hello) {
            hello();
        } else {
            // Error code here
        }
    }
    return 0;   
}

dllmain.cpp

#include "dll.h"
#include <windows.h>

DLLIMPORT void hello()
{
   MessageBox(NULL, "Hey", "", MB_OK);          
}

DllClass::DllClass()
{

}

DllClass::~DllClass ()
{

}


BOOL APIENTRY DllMain (HINSTANCE hInst     /* Library instance handle. */ ,
                       DWORD reason        /* Reason this function is being called. */ ,
                       LPVOID reserved     /* Not used. */ )
{
    switch (reason)
    {
        case DLL_PROCESS_ATTACH:
        break;

        case DLL_PROCESS_DETACH:
        break;

        case DLL_THREAD_ATTACH:
        break;

        case DLL_THREAD_DETACH:
        break;
    }

    /* Returns TRUE on success, FALSE on failure */
    return TRUE;
}

dll.h

#ifndef _DLL_H_
#define _DLL_H_

#if BUILDING_DLL
# define DLLIMPORT __declspec (dllexport) void hello(void)
#else /* Not BUILDING_DLL */
# define DLLIMPORT __declspec (dllexport) void hello(void)
#endif /* Not BUILDING_DLL */

class DLLIMPORT DllClass
{
    public:
    DllClass();
    virtual ~DllClass(void);

    // Says hello world
    DLLImport void hello(void);

    private:

};


#endif /* _DLL_H_ */

I’d like to know what I’m doing wrong so I can document it and learn.

Thanks

Answer 1

You need to put your DLL code in an extern "C" block, otherwise the compiler will mangle the names of all functions.

Take a look at this question for further info:
C++ DLL Export: Decorated/Mangled names