Question

I am a C/C++ programmer, but I was asked to update a program that was written in C# to communicate with a device. My knowledge of C# is very basic.

The previous version was totally written in C#, but now the API that in fact access the device was changed to C. I found out that I can import the C function APIs by using:

[DllImport("myapi.dll")]
public static extern int myfunct( 
                                 [MarshalAs(UnmanagedType.LPTStr)] string lpDeviceName,
                                 IntPtr hpDevice);

In C this function prototype is:

int myFunct( LPTStr lpDeviceName, HANDLE* hpDevice );

Where HANDLE is defined as :

typedef void *HANDLE;

However this function does not work as expected. In fact, in the C# code call what kind of type I should declare and pass to the C# method?

Thanks for the help and sorry for any stupid question.

Answer 1

you are passing IntPtr instead of ref IntPtr, the definition should look like this:

[DllImport("myapi.dll")]
public static extern int myfunct( 
    [MarshalAs(UnmanagedType.LPTStr)] string lpDeviceName,
    ref IntPtr hpDevice);