Cannot Load C++ DLL in C#

Question

Hello,

>My previous thread<

I created this one,because I installed WinXP on VMBox and I cannot get it working again.

This time I created an OnLoad Event on my form

        if (LoadLibrary("blowfish.dll") == 0)
        {
            Misc.LogToFile("Could not load dll", true);
            Application.Exit();
        }

Runs fine on my PC,but on VMBox LoadLibrary returns 0.

Some users mentioned that the problem would be in mixing older NET Framework(2.0) with dlls made on newest MS Visual studio(2008 SP1) so I took action and now the program properties it's set to work with NET 3.5

On the VMBox I have NET 2.0,but this is not the problem - the program itself runs fine.I also have C++ Redistributable(2005,2005 SP1 and 2008).

What could be the problem?

Answer 1

It could be that the dll's location is on the path in one environment and not in the other. It could also be permissions in one environment are not the same as the other.

Answer 2

Try running dependency walker on the DLL - see if any modules are missing.

Answer 3

Call GetLastError after LoadLibrary, check the error code value here: http://msdn.microsoft.com/en-us/library/ms681381.aspx and see if that helps.

Answer 4

To further trouble should you could call

Marshal.GetLastWin32Error();

which should give you an error code.

Is it possible that you deployed a debug version of your native dll which also requires a debug version of MSVCR90**D**.DLL? You should have distributed the release version because the debug version requires a different set of dlls to be present on the target system.

It obviously works on your development machine because all debug versions of the required libraries come with Visual Studio.

This is how you would get the message belonging to an error code:

[DllImport("kernel32.dll")]
private unsafe static extern int FormatMessage(int dwFlags, 
    int lpSource, int dwMessageId, int dwLanguageId, 
    ref String lpBuffer, int nSize, int Arguments);

public static string GetErrorMessage(int errorCode)
{
    int FORMAT_MESSAGE_ALLOCATE_BUFFER = 0x00000100;
    int FORMAT_MESSAGE_IGNORE_INSERTS = 0x00000200;
    int FORMAT_MESSAGE_FROM_SYSTEM  = 0x00001000;

    int messageSize = 255;
    string lpMsgBuf = "";
    int dwFlags = FORMAT_MESSAGE_ALLOCATE_BUFFER 
       | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS;

    int retVal = FormatMessage(dwFlags, 0, errorCode, 0, 
                               ref lpMsgBuf, messageSize, 0);
    if (0 == retVal) 
    {
        return null;
    }
    else
    {
        return lpMsgBuf;
    }
}