BadImageFormatException error when using C++ .dll function for C#?

I am having trouble with using P/Invoke for C#. Here is the function (written in C++) that I am trying to call from the .dll:

string
BeatTracker::getName() const
{
    return "Tempo and Beat Tracker";
}

And here is my code for trying to call this function:

[DllImport("qm-vamp-plugins.dll",EntryPoint="BeatTracker")]
public static extern string getName();

public QMTempo(开发者_运维技巧)
{
   Console.WriteLine(getName());
}

What seems to be wrong? I am getting a BadImageFormatException. And how can I know what is wrong in future references aside from the vague names the IDE is giving me? I am using Visual Studio 2008 by the way.

Also I am using (but not sure if right) EntryPoint, to let it know that I am using the getName function from the BeatTracker class (because there are also getName functions for other classes, which are included in the single .dll file)

Thanks!

This exception can be caused by a mismath between the .NET runtime proc architecture used and the imported dll one.

More precisely:

Do you use a 64bit Windows? The runtime will, by default, run in 64bit. If your C++ library was compiled targeting 32bit, you will get a BadFormatException upon library loading. The Same goes if your .NET app is running 32bit and your C++ library was compiled targeting x64.

If you can recompile the library, do it. Otherwise you can force the .NET runtime to use a specified architecture at compilation, but it will prevent it from running on the other architecture. It's your choice ;) When coding against .NET or java, we tend to forget what really happen under the hood.

[DllImport("qm-vamp-plugins.dll",EntryPoint="BeatTracker")]

The EntryPoint should be getName(), not BeatTracker which is a class!

But even then you cannot call that, because getName() is member function which cannot be callled without instance.

So I would suggest that define free functions in the DLL, and export them. You can use class internally, in the DLL. You can work with handle of classes.

Example,

DLL code:

typedef BeatTracker* PBeatTracker;
typedef PBeatTracker HBeatTracker; 

//exported functions
HBeatTracker CreateBeatTracker()
{
      return new BeatTracker();
}
void DeleteBeatTracker(HBeatTracker  handle)
{
     delete handle;
}
string getName(HBeatTracker handle)
{
    return handle->getName();
}

C# Code:

[DllImport("qm-vamp-plugins.dll",EntryPoint="CreateBeatTracker")]
public static extern IntPtr CreateBeatTracker();

[DllImport("qm-vamp-plugins.dll",EntryPoint="DeleteBeatTracker")]
public static extern void DeleteBeatTracker(IntPtr);

[DllImport("qm-vamp-plugins.dll",EntryPoint="getName")]
public static extern string getName(IntPtr);

public QMTempo()
{
   IntPtr handle = CreateBeatTracker();
   Console.WriteLine(getName(handle));
   DeleteBeatTracker(handle);
}