include .h files

thx it works now, but i dont have the IntPtr Parameter = Marshal.AllocCoTaskMem( Marshal.SizeOf( abc ) ); Marshal.StructureToPtr(abc, Parameter, false); lines, because i'll get an error if i insert them :)

I see this all the time. Most of the Win32 API is not yet available in the .NET framework. What little is available, you'll want to use. Some of the functions that are in windows.h are available in C# without using interop. If you specify the function, we can tell you if there is an object in the FCL that does it for you.

[DllImport("THEFUNCTIONLIBRARY.dll")] private static extern bool THEFUNCTION(IntPtr var); [ StructLayout( LayoutKind.Sequential )] private struct STRUCT_ABC { public uint var1; public uint var2; } STRUCT_ABC abc; abc.var1=1; abc.var2=2; IntPtr Parameter = Marshal.AllocCoTaskMem( Marshal.SizeOf( abc ) ); Marshal.StructureToPtr(abc, Parameter, false); THEFUNCTION(Parameter); // forgot to include info about FreeCoTaskMem() in the above post // Since you are allocating unmanaged memory, you must free it or else // there will be a nice memory leak. Marshal.FreeCoTaskMem(lParam);

thank u very much ... i read all, but i dont understand it 100% probably u can show me the working code for this sample: // the structure: typedef struct _ABC ( DWORD var1; DWORDLONG var2; ) ABC, *LPABC; // the function: bool THEFUNCTION( LPABC var ); so how does the c# code look like? and how can i call the function with the struct? pls help, its really important :)

Well, you're going to hate the answer if you're using them all over the place. You have to declare them yourself. I use sendmessage a lot. Its signature in the namespace (put it outside of a class but in a namespace) is this: [DllImport("user32.dll")] private static extern Int32 SendMessage(IntPtr hWnd, Int32 msg,Int32 wParam, IntPtr lParam); Just change the dll it is exported from, the return type, name of the function, and the parameters to reflect the function you're using. Also, if your function uses a certain structure, you have to declare the structure as well, like so: [ StructLayout( LayoutKind.Sequential )] private struct STRUCT_RECT { public Int32 left; public Int32 top; public Int32 right; public Int32 bottom; } Then, finally, to use a struct in your imported, unmanaged function, you must do the following. STRUCT_RECT r; r.left=0; r.top=0; r.right=100; r.bottom=100; IntPtr lParam = Marshal.AllocCoTaskMem( Marshal.SizeOf( r ) ); Marshal.StructureToPtr(r, lParam, false); SendMessage(WindowHandle,0x1234,0,lParam); ... Keep in mind that in addition to all that stuff, 0x1234 is a constant that you looked up in windows.h or whatever header file. You can optionally declare it a private const int in your class, but that may just add bloat to a class you use all too often. The choice is up to you. This is a tedious process and isn't for the faint of heart but I understand why you need this, I migrated from win32/c++ not too long ago. Use the C# classes when you can. Good luck.