How do I invoke this native method from C#

I want to invoke one/many functions of a native library but I am unsure on the type mappings. The function in particular I am currently trying is as follows, here is the small console app which I am spiking in:

extern char *tgetstr (const char *name, char **area);

And here is my attempt at mapping this to use in a .NET console. I get an error saying, trying to read or write protected memory.

class Program
{
    [DllImport("termcap.dll")]
    public static extern IntPtr tgetstr(IntPtr name, IntPtr area);

    static void Main(string[] args)
    {
        IntPtr ptr1 = new IntPtr();
        IntPtr a = tgetstr(Marshal.StringToCoTaskMemAnsi("cl"), ptr1);
        Console.WriteLine(Marshal.PtrToStringBSTR(a));
    }
}

TIA

A开发者_开发知识库ndrew

You need to pass your IntPtr by ref, so the function can overwrite it. Then you also need to free the string after you've copied it, hopefully the DLL provides a matching deallocation function. StringToCoTaskMemAnsi isn't helping you any either, it's just leaking memory.

The correct p/invoke declaration is probably

[DllImport("termcap.dll", CharSet = CharSet.Ansi)]
public static extern IntPtr tgetstr(string name, ref IntPtr area);

I haven't worked with unmanaged code since 3 years but I think you can do it by marking the method parameters with MarshalAs attribute. Check this article,

MSDN

You have to pin your ptr1.

GCHandle handle = GCHandle.Alloc(ptr1, GCHandleType.Pinned);