unsigned char ** equivalent in c# and have to write the return value in a file

Question

I have to call a win32 dll function

int func1( int arg1, unsigned char **arg2, int *arg3);

and i need wrapped in c# as

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Answer 1

i have a free function in the dll to clear the memory

Then you have a shot at making this work. The function declaration ought to look like this:

[DllImport("foo.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern int func1(int arg1, out IntPtr arg2, ref int arg3);

And you'd call it like this:

IntPtr ptr = IntPtr.Zero;
int dunno = 99;
string result = null;

int retval = func1(42, out ptr, ref dunno);
if (retval == success) {
    result = Marshal.PtrToStringAnsi(ptr);
    // etc...
}
if (ptr != IntPtr.Zero) func1free(ptr);

Where "func1free" is the otherwise undocumented function that releases the string.

Answer 2

You probably need to use the MarshalAs attribute, for example:

public static extern int func1(int arg1, [MarshalAs(UnmanagedType.LPStr)] string arg2, IntPtr arg3);

Check here for documentation:

http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.marshalasattribute.aspx