I need to use an unmanaged COM dll in c# program. Dll contains a function, say:
Open(char *name);
But when imported to c# (Project->Add Reference) it is available as:
mydll.Open(ref byte name)
How can I pass a string to this function?
When I do:
byte[] name = new byte[32];
mydll.Open(ref name);
I get compilation error "Cannot convert ref byte[] to ref byte".
If you mean for it to be a string, then in your IDL file, you have to specify that this point represents a string. See this article for information on the [string] attribute: http://msdn.microsoft.com/en-us/library/d9a4wd1h%28v=VS.80%29.aspx If you want to be CLS compliant (and interoperate with scripting languages, you might want to look into using BSTR instead of char* for passing strings). This way you'll get unicode support too.
Unless you give COM the hint that this is a string, you will have problems whenever COM has to marshal the parameters (i.e. across apartment or process boundaries).
This article may also give you a good starting point on C++ / C# / COM goodies: COM Interop Part 1: C# Client Tutorial
[in, string] wchar_t* took care of my issue.Maybe you can do this...
byte[] bytes = Encoding.ASCII.GetBytes(myString);
You might try decorating that "name" variable with:
[System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPStr)]
That's a single byte, and I think is compatibel with a single char. If not, the answer is likely going to be using MarshalAs to make that variable look like type.
Keep in mind you could lose it if the array is not properly terminated. Anyhow, I would try passing in the pointer to the first element byte[0] try:
mydll.Open(ref name[0]);
I'm not sure how the interop will marshal this but it's worth a try.
The import is not correct. You can import it manually:
[DllImport("<Your COM Dll>")]
private static extern <Return Type> <"Function Name">();
Then, in your main method, or in the method where you initialize your dll object, you need:
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
private static extern IntPtr LoadLibrary(string lpFileName);
public MyDll()
{
Environment.CurrentDirectory = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
string dllPath = Environment.CurrentDirectory + @"<Location of Dll you are importing from>";
LoadLibrary(dllPath);
}
For example, check out the following COM Dll:
GOIO_DLL_INTERFACE_DECL gtype_int32 GoIO_GetNthAvailableDeviceName(
char *pBuf,
gtype_int32 bufSize,
gtype_int32 vendorId,
gtype_int32 productId,
gtype_int32 N);
I imported this Dll as the following:
[DllImport("GoIO_DLL.dll")]
private static extern int GoIO_GetNthAvailableDeviceName(
byte[] pBuf,
int bufSize,
int vendorId,
int productId,
int N);
As you can see, the char pointer becomes a byte[], just like you tried. There is no need for the ref keyword.
