[RESOLVED] LoadLibrary returns 0

[funkmonkey]

Hi, I'm trying to generate a DLL that is just a simple timer like routine for activating when a System DLG box pops up. I am unable to get anything but 0 from the library. I have checked the code, but I don't see the issue. It would be great if someone could point out where my issue lies. Here is the C++/H code.

// 
#include "pch.h" // use stdafx.h in Visual Studio 2017 and earlier
#include <utility>
#include <Windows.h>
#include <synchapi.h>
#include "EPIQ Util.h"




// DLL internal state variables:
static BOOL bTimerOn;  // Turns on/off the timer
static BOOL bRunning;  // Keeps us in the while loop
static unsigned long ulWait; // How long to wait

//void EPIQ_ExecuteTimer();
//void EPIQ_SetTimer();
//void EPIQ_init(const unsigned long);
//void EPIQ_StopTimer();
//void EPIQ_StartTimer();

// Initialize the Timer variables
void EPIQ_init(const unsigned long ullWait)
{
    bTimerOn = FALSE;
    ulWait = ullWait;

    MessageBox(NULL, (LPCWSTR) "Made it here", (LPCWSTR) "We made it", NULL);

    return;
}



// Stop the timer from running
void EPIQ_StopTimer()
{
    bTimerOn = FALSE;
    Sleep(ulWait);
    return;
}

// Start the timer from running
void EPIQ_StartTimer()
{
    bTimerOn = TRUE;
    return;
}

//The actual process of the timer
void EPIQ_TimerProc()
{

    //create two structures to hold our Main Window handle
    //and the Button's handle
    HWND WindowHandle;
    HWND ButtonHandle;


    //this window's caption is "File Download", so we search for it's handle using the FindWindow API		
    WindowHandle = FindWindow(NULL, (LPCWSTR) "Message from webpage");

    SetForegroundWindow(WindowHandle);

    //the Button's Caption is "OK" and it is a "Button".  SPYXX.exe that comes with Microsoft Visual Studio will reveal this information to you
    ButtonHandle = FindWindowEx(WindowHandle, 0, (LPCWSTR) "Button", (LPCWSTR) "OK");

    //send a message to the button that you are "clicking" it.  Surprisingly C++ understands what BM_CLICK is without having to set it.  Different than VB
    SendMessage(ButtonHandle, BM_CLICK, 0, 0);

    return;
}




#pragma once
// EPIQ_Util.h - Contains declarations of Utility Functions
#pragma once

#ifdef EPIQUTIL_EXPORTS
#define EPIQUTIL_API __declspec(dllexport)
#else
#define EPIQUTIL_API __declspec(dllimport)
#endif

// The functions needed to interface with VBA EPIQ_Interface

// This function must be called before any other function.
extern "C" EPIQUTIL_API void EPIQ_init(const unsigned long);

// Set how long to wait in ms.
extern "C" EPIQUTIL_API void EPIQ_SetTimer();

// Perform the TimerProc function.
extern "C" EPIQUTIL_API void EPIQ_ExecuteTimer();

// disable the timer.
extern "C" EPIQUTIL_API void EPIQ_StopTimer();

// Start the Timer
extern "C" EPIQUTIL_API VOID EPIQ_StartTimer();

extern "C" EPIQUTIL_API void EPIQ_TimerProc();

//extern "C" EPIQUTIL_API HWND SetActiveWindow Lib "user32.dll" (HWND hwnd);

int SetForegroundWindow (int hwnd);


int SetActiveWindow(int hwnd);

[2kaud]

You don't say what is 0. However you're not checking the return value from FindWindow()/FindWindowEx() which are NULL if not found.

[John E]

And shouldn't the OP's wide character strings be like this:-

L"Button"

L"Message from webpage"

etc ??

[funkmonkey]

You don't say what is 0. However you're not checking the return value from FindWindow()/FindWindowEx() which are NULL if not found.

Sorry..... That is the return value from LoadLibrary. The library is not able to load the DLL, and I'm not seeing why. Any suggestions?

[funkmonkey]

And shouldn't the OP's wide character strings be like this:-

L"Button"

L"Message from webpage"

etc ??

Did not know that. Usually in the past, years and years ago, the test was cast to (LPCWSTR). I have not been in C++ since about 2000, so I'm a lot rusty. Been working mostly with VBA. Thanks for the information, will adapt as noted.

[funkmonkey]

     Dim ProcAdd As LongPtr
    Dim hinstLib As Long
    
 
    ' Get a handle to the DLL module.
        hinstLib = LoadLibrary("C:\Users\epperbx\source\repos\EPIQ Util\x64\Debug\EPIQ Util.dll")

Any ideas why this would be returning 0 would be greatly appreciated. I'm at my witts end. I've tried hinstLib with LongPtr, VBA, as well and that did not make any difference.

I just don't see the issue. I have generated a blank project and still get (0) from LoadLibrary.

[funkmonkey]

     Dim ProcAdd As LongPtr
    Dim hinstLib As Long
    
 
    ' Get a handle to the DLL module.
        hinstLib = LoadLibrary("C:\Users\epperbx\source\repos\EPIQ Util\x64\Debug\EPIQ Util.dll")

Any ideas why this would be returning 0 would be greatly appreciated. I'm at my witts end. I've tried hinstLib with LongPtr, VBA, as well and that did not make any difference.

I just don't see the issue. I have generated a blank project and still get (0) from LoadLibrary.

FINALLY got this to work. Now I'm having similar issues with GetProcAddress always returning a (0). Below is the function call. Anyone see anything I'm missing here in the call?

    Dim ProcAdd As LongPtr
    Dim hinstLib As LongPtr
    Dim hFreeLib As LongPtr
    
 
    ' Get a handle to the DLL module.
        hinstLib = LoadLibrary("C:\Users\epperbx\source\repos\_EPIQ Util DLL_\Debug\EPIQ Util.dll")
 
        ' If the handle is valid, try to get the function address.
    
        
            ProcAdd = GetProcAddress(hinstLib, "EPIQ_Init")

Any ideas will hopefully save me hours of hair pulling.

[2kaud]

Shouldn't \ inside " be \\ ? It should be in c++ but vb??

hinstLib = LoadLibrary("C:\\Users\\epperbx\\source\\repos\\_EPIQ Util DLL_\\Debug\\EPIQ Util.dll")

[salem_c]

> Shouldn't \ inside " be \\ ?

No idea.
The OP seems to be wandering between C++ and VB on a per-post basis.

> Now I'm having similar issues with GetProcAddress always returning a (0).
Well call GetLastError.
https://learn.microsoft.com/en-us/wi...i-getlasterror

Then you might find something better to report than "it doesn't work".


> ProcAdd = GetProcAddress(hinstLib, "EPIQ_Init")
Yeah, Init is in lower case in your most recent C++ code.

Unlike the rest of the functions which are EPIQ and then a capital.

[2kaud]

You can also use DUMPBIN to see what actually is being exported in the .dll file:

dumpbin /exports C:\Users\epperbx\source\repos\_EPIQ Util DLL_\Debug\EPIQ Util.dll

[funkmonkey]

Shouldn't \ inside " be \\ ? It should be in c++ but vb??

hinstLib = LoadLibrary("C:\\Users\\epperbx\\source\\repos\\_EPIQ Util DLL_\\Debug\\EPIQ Util.dll")

Thanks for the input. I did not have to do the double slashes to get the code to finally load the dll. Not sure what the fixe was, as I compiled multiple times after minor tweeks to try and get the library to load. I'm just glad the LoadLibrary function works. Now I get to fight with GetProcAddress. Since the loadlibrary is working I'm focusing in on the DLL side, only makes sense to me.

Anything seen from the calling Code above that looks out of place? I'm off to fiddle with the DLL side to see what I can find as to why the function can't pull in the address of the function.

Thanks for your input.

[2kaud]

Thanks for the input. I did not have to do the double slashes to get the code to finally load the dll. Not sure what the fixe was, as I compiled multiple times after minor tweeks to try and get the library to load. I'm just glad the LoadLibrary function works. Now I get to fight with GetProcAddress. Since the loadlibrary is working I'm focusing in on the DLL side, only makes sense to me.

Anything seen from the calling Code above that looks out of place? I'm off to fiddle with the DLL side to see what I can find as to why the function can't pull in the address of the function.

Thanks for your input.

As I mentioned above, first use DUMPBIN to see what is actually being exported from the dll

[funkmonkey]

As I mentioned above, first use DUMPBIN to see what is actually being exported from the dll

Thanks. I tried to run DUMPBIN in a Command Prompt but it is not recognized. Does it get run from Visual Studio? I have not come across it yet in my search. I'm using VS 2022.

[2kaud]

See https://learn.microsoft.com/en-us/cp...?view=msvc-170 for info about dumpbin and how it's used.

[Igor Vartanov]

#ifdef EPIQUTIL_EXPORTS
#define EPIQUTIL_API __declspec(dllexport)
#else
#define EPIQUTIL_API __declspec(dllimport)
#endif

My best guess is EPIQUTIL_EXPORTS is not defined when the DLL gets built, thus no exporting occurs.