Unmanaged Code (written in C++) Interop with C#

Hi,

I am trying to write a wrapper in C# for the unmanaged code written in C++. Whats wrong in the following code.

C++ (Unmanaged Code)

extern int DllExport __stdcall GetName( LPSTR name)
{
   name = "Smith, Allan";
   strcat( name, "\0");
   return strlen( name);
}

Wrapper Definition (Written in C#)
[DllImport("Unmanaged.Dll", SetLastError=true, ThrowOnUnmappableChar=true, EntryPoint="GetName)] public static extern int GetName( [MarshalAs(UnmanagedType.LPStr)] string name);

Wrapper function (written in C#)
public static int GetName( string name)
{
   int rc;
   rc = Wrapper.GetName( name);
   return rc;
}

When I run this function, Wrapper.GetName function returns 12 (length of Smith, Allen). But the variable name is still blank.

Please help me.

Thanks
Raja

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Unmanaged Code (written in C++) Interop with C#

Jublar
>> But I would like to know how it get it working with LPSTR...

Use the CharSet in DllImport to enable ASCII format.
tinu44
Use System.Text.StringBuilder instead of string.
WebSnozz

Surely you need to pass your string in as a ref parameter ( whatever you need to do to the dll to make that work )
Eyfel
I had to make few changes to the above code. It is working now.

C++ (Unmanaged Code)

extern int DllExport __stdcall GetName( LPTSTR name)
{
   name = "Smith, Allan";
   strcat( name, "\0");
   return strlen( name);
}

I had to declare "LPSTR name" as "LPTSTR name" in the above unmanaged function.

Wrapper Definition (Written in C#)
[DllImport("Unmanaged.Dll", SetLastError=true, ThrowOnUnmappableChar=true, EntryPoint="GetName)] public static extern int GetName( StringBuilder name);

I had to change the "[MarshalAs(UnmanagedType.LPStr)] string " to "StringBuilder"

Wrapper function (written in C#)
public static int GetName( string name)
{
   int rc;
   rc = Wrapper.GetName( name);
   return rc;
}

I changed the above function to ...

public static int GetName( ref string name)
{
   int rc;
   StringBuilder sb = new StringBuilder( 256);
   rc = Wrapper.GetName( sb);
   name = sb.ToString( );
   return rc;
}

It is working now. But I would like to know how it get it working with LPSTR...

Thanks for your help.

Raja
Pete A
Sorry, I was wrong. I am passing the string argument as ref.
Unmanaged Code (written in C++) Interop with C#

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