Delphi2005学习笔记2——Using Platform Invoke with Delphi 2005

NULL characters. Since the default marshaler will consider the first NULL to be the end of the string, the data will be truncated (this also applies to the StringToHGlobalXXX and PtrToStringXXX methods). In this situation TBytes can be used (using the PlatformStringOf and PlatformBytesOf functions in Borland.Delphi.System to convert the byte array to/from a string). Note that these utility functions do not add or remove terminating NULL characters. When working with COM interfaces, the UnmanagedType enumeration (used by the MarshalAsAttribute class) has a special value, LPStruct. This is only valid in combination with a System. Guid class, causing the marshaler to convert the parameter into a Win32 GUID structure. The function CoCreateInstance that is declared in Delphi 7 as:

function CoCreateInstance([MarshalAs(UnmanagedType.LPStruct)] clsid: TCLSID;
  [MarshalAs(UnmanagedType.IUnknown)] unkOuter: TObject; 
  dwClsContext: Longint; 
  [MarshalAs(UnmanagedType.LPStruct)] iid: TIID;
  [MarshalAs(UnmanagedType.Interface)] out pv
): HResult;

This is currently the only documented use for UnmanagedType.LPStruct. Structures The biggest difference between calling unmanaged functions and passing structures to unmanaged functions is that the default marshaler has some major restrictions when working with structures. The most important are that dynamic arrays, arrays of structures and the StringBuilder class cannot be used in structures. For these cases IntPtr is required (although in some cases string paired with various marshaling attributes can be used for strings). Data Types The following table shows commonly used data types, and how to “translate” them for managed code: Unmanaged Data Type Managed Data Type Input Parameter Output Parameter Pointer to string (PChar) String IntPtr Character array (array[a..b] of Char) String String Array of value type (array[a..b] of Byte) array[a..b] of Byte array[a..b] of Byte Dynamic array (array[0..0] of type) IntPtr IntPtr Array of struct (array[1..2] of TRect) IntPtr or flatten IntPtr or flatten Pointer to structure (PRect) IntPtr IntPtr Pointer to simple type (PByte) IntPtr IntPtr Pointer to array (PInteger) IntPtr IntPtr

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