how to use a third party dll

[sam1900]

hi
i want to call some functions from a DLL(which is provided by a hardware manufacturer without the .lib and .def). I've used these following code

  HINSTANCE hinstLib; 
    MYPROC ProcAdd=NULL; 
    BOOL fFreeResult, fRunTimeLinkSuccess = FALSE; 
 
    // Get a handle to the DLL module.
 
    hinstLib = LoadLibrary(TEXT("C:\My.dll")); 
 
    // If the handle is valid, try to get the function address.
 
    if (hinstLib != NULL) 
    { 
        std::cout<<"loaded\n";
 
 
 
 ProcAdd = (MYPROC) GetProcAddress(hinstLib, "funcinDLL");
 
 // If the function address is valid, call the function.
 
        if (NULL != ProcAdd) 
        {
            fRunTimeLinkSuccess = TRUE;
            (*ProcAdd) (); 
        }
        // Free the DLL module.
 
        fFreeResult = FreeLibrary(hinstLib); 
    } 
 
    // If unable to call the DLL function, use an alternative.
    if (! fRunTimeLinkSuccess) 
        printf("Message printed from executable\n"); 
 

but LoadLybrary is failing to load the DLL..
can anyone suggest me , how can i do the job?

[Banfa]

When LoadLibrary fails it must be for a reason. Assuming that you have the path correct I suggest you call and print the return value from GetLastError to get some clarificaion of what is causing the problem.

You can look up the value returned from GetLastError in winerror.h

[weaknessforcats]

Your path to the dll must be C:\\My.dll. The \ is an escape character so you need \\ to get an actual \ in your path.

Also, the function name used by GetProcAddress must be exported by the DLL and if the DLL is written in C++ that must also be an extern "C" function.

[sam1900]

hi
thanks for your reply.
i used the following code to get the last error code.

LPTSTR lpszFunction=TEXT("GetProcessId");
LPVOID lpMsgBuf;
LPVOID lpDisplayBuf;
DWORD dw = GetLastError();

FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_IGNORE_INSERTS,
NULL,
dw,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR) &lpMsgBuf,
0, NULL );
std::cout<<"enter2\n";
// Display the error message and exit the process

lpDisplayBuf = (LPVOID)LocalAlloc(LMEM_ZEROINIT,
(lstrlen((LPCTSTR)lpMsgBuf) + lstrlen((LPCTSTR)lpszFunction) + 40) * sizeof(TCHAR));
StringCchPrintf((LPTSTR)lpDisplayBuf,
LocalSize(lpDisplayBuf) / sizeof(TCHAR),
TEXT("%s failed with error %d: %s"),
lpszFunction, dw, lpMsgBuf);
MessageBox(NULL, (LPCTSTR)lpDisplayBuf, TEXT("Error"), MB_OK);
std::cout<<"enter3\n";
LocalFree(lpMsgBuf);
LocalFree(lpDisplayBuf);
ExitProcess(dw);
But it didn't print the error code

[sam1900]

hi
thanks for your reply.
the DLL is in VC++. I didn't get that you have said about the path. The actual location of the dll is
C:\Documents and Settings\hexapod\Desktop\cyton_important\My.dll
i used this path in the LoadLibrary.
i kept a copy of the dll in project folder also.

[weaknessforcats]

You have to call GetLastError() immediately after the function:

AWindowsFunnction();
DWORD dw = GetLastError();

to get the error from AWindowsFunction.


This path:

C:\Documents and Settings\hexapod\Desktop\cyton_important\My.dll

is seen by the compiler as:

C:ocuments and Settingsexapodesktopyton_importanty.dll

because the \ is the escape sequence. That means the character after the \ is a code and not a separate character. Like \n means newline character and not a \ followed by an n.

You have to code \\ to tell the compiler that the code is \.

Therefore:

C:\\Documents and Settings\\hexapod\\Desktop\cyton_important\\My.dll

compiles to:

C:\Documents and Settings\hexapod\Desktop\cyton_important\My.dll

which is what you want.