[Mono-list] Need help with DllImport (P/Invoke) and UCS-4 unicode

Christian Heimes lists at cheimes.de
Mon Jul 16 11:06:54 EDT 2007

Jonathan Pryor wrote:
[great stuff]

Thank you very much Jonathan! You and the other Jonathan are extremely
helpful. On the other hands the docs from MSDN aren't very helpful at
all. :(

Your code works like a charm and I got most unit tests running. I'm
still having a small problem. How can I apply a custom marshaler to the
return value of a pinvoke? I like to replace some code with the custom

    [DllImport(Runtime.dll, CallingConvention = CallingConvention.Cdecl,
           EntryPoint = "PyUnicodeUCS4_AsUnicode",
           ExactSpelling = true)]
    internal unsafe static extern char*
    PyUnicode_AsUnicode(IntPtr ob);

    internal unsafe static string GetManagedString(IntPtr op) {
        IntPtr type = PyObject_TYPE(op);


        if (type == Runtime.PyUnicodeType) {
            char *p = Runtime.PyUnicode_AsUnicode(op);
            int size = Runtime.PyUnicode_GetSize(op);
            return new String(p, 0, size);

        return null;

> This uses the Mono.Unix.UnixMarshal class within Mono.Posix.dll.
> For a custom marshaler, your DllImport would be:
>         [DllImport(Runtime.dll, CallingConvention = CallingConvention.Cdecl)]
>         internal unsafe static extern IntPtr
>         PyUnicode_FromUnicode(
>                 [MarshalAs (UnmanagedType.CustomMarshaler, 
>                  MarshalTypeRef=typeof(Utf32Marshaler)]
>                 string path, int size);

Note: You forgot a closing bracket. ;)


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