Platform Invoke

Finally ,找到工具来参考转换。

Source: https://github.com/jaredpar/pinvoke
Tool: https://archive.codeplex.com/?p=clrinterop

书籍 参考：

NET and COM: The Complete Interoperability Guide

https://docs.microsoft.com/en-us/cpp/dotnet/calling-native-functions-from-managed-code

这篇新文章里面有详细的解释，包括数据类型的转换。

还可以参考这个文档：

file:///C:/Users/wiyan/AppData/Local/Microsoft/Windows/INetCache/IE/Q0DGUWJP/traks_computerscience_2016.pdf

Marshaling Arguments

With PInvoke, no marshaling is needed between managed and C++ native primitive types with the same form. For example, no marshaling is required between Int32 and int, or between Double and double.

However, you must marshal types that do not have the same form. This includes char, string, and struct types. The following table shows the mappings used by the marshaler for various types:

wtypes.h	Visual C++	Visual C++ with /clr	Common language runtime
HANDLE	void *	void *	IntPtr, UIntPtr
BYTE	unsigned char	unsigned char	Byte
SHORT	short	short	Int16
WORD	unsigned short	unsigned short	UInt16
INT	int	int	Int32
UINT	unsigned int	unsigned int	UInt32
LONG	long	long	Int32
BOOL	long	bool	Boolean
DWORD	unsigned long	unsigned long	UInt32
ULONG	unsigned long	unsigned long	UInt32
CHAR	char	char	Char
LPCSTR	char *	String ^ [in], StringBuilder ^ [in, out]	String ^ [in], StringBuilder ^ [in, out]
LPCSTR	const char *	String ^	String
LPWSTR	wchar_t *	String ^ [in], StringBuilder ^ [in, out]	String ^ [in], StringBuilder ^ [in, out]
LPCWSTR	const wchar_t *	String ^	String
FLOAT	float	float	Single
DOUBLE	double	double	Double

PInvoke 允许managed code 来调用在DLL中实施的unmanged function。

Platform invoke relies on metadata to locate exported functions and marshal their arguments at run time. The following illustration shows this process.

A platform invoke call to an unmanaged DLL function

When platform invoke calls an unmanaged function, it performs the following sequence of actions:

1. Locates the DLL containing the function.
2. Loads the DLL into memory.
3. Locates the address of the function in memory and pushes its arguments onto the stack, marshaling data as required.
   

   Note   Locating and loading the DLL, and locating the address of the function in memory occur only on the first call to the function.

4. Transfers control to the unmanaged function.

Platform invoke throws exceptions generated by the unmanaged function to the managed caller.

There are two ways that C# code can directly call unmanaged code:

• Directly call a function exported from a DLL.
• Call an interface method on a COM object (for more information, see COM Interop Part 1: C# Client Tutorial).

For both techniques, you must provide the C# compiler with a declaration of the unmanaged function, and you may also need to provide the C# compiler with a description of how to marshal the parameters and return value to and from the unmanaged code.

Calling a DLL Export Directly from C#

To declare a method as having an implementation from a DLL export, do the following:

• Declare the method with the static and extern C# keywords.
• Attach the DllImport attribute to the method. The DllImport attribute allows you to specify the name of the DLL that contains the method. The common practice is to name the C# method the same as the exported method, but you can also use a different name for the C# method.
• Optionally, specify custom marshaling information for the method's parameters and return value, which will override the .NET Framework default marshaling.

Example 1

This example shows you how to use the DllImport attribute to output a message by calling puts from msvcrt.dll.

 

 

// PInvokeTest.cs
using System;
using System.Runtime.InteropServices;

class PlatformInvokeTest
{
    [DllImport("msvcrt.dll")]
    public static extern int puts(string c);
    [DllImport("msvcrt.dll")]
    internal static extern int _flushall();

    public static void Main()
    {
        puts("Test");
        _flushall();
    }
}

Output

 

 

Test

Code Discussion

The preceding example shows the minimum requirements for declaring a C# method that is implemented in an unmanaged DLL. The method PlatformInvokeTest.puts is declared with the static and extern modifiers and has the DllImport attribute which tells the compiler that the implementation comes from msvcrt.dll, using the default name of puts. To use a different name for the C# method such as putstring, you must use the EntryPoint option in the DllImport attribute, that is:

 

 

[DllImport("msvcrt.dll", EntryPoint="puts")]

For more information on the syntax of the DllImport attribute, see DllImportAttribute Class.

Default Marshaling and Specifying Custom Marshaling for Parameters to Unmanaged Methods

When calling an unmanaged function from C# code, the common language runtime must marshal the parameters and return values.

For every .NET Framework type there is a default unmanaged type, which the common language runtime will use to marshal data across a managed to unmanaged function call. For example, the default marshaling for C# string values is to the type LPTSTR (pointer to TCHAR char buffer). You can override the default marshaling using theMarshalAs attribute in the C# declaration of the unmanaged function.

Example 2

This example uses the DllImport attribute to output a string. It also shows you how to override the default marshaling of the function parameters by using the MarshalAsattribute.

 

 

// Marshal.cs
using System;
using System.Runtime.InteropServices;

class PlatformInvokeTest
{
    [DllImport("msvcrt.dll")]
    public static extern int puts(
        [MarshalAs(UnmanagedType.LPStr)]
        string m);
    [DllImport("msvcrt.dll")]
    internal static extern int _flushall();

    public static void Main()
    {
        puts("Hello World!");
        _flushall();
    }
}

Output

When you run this example, the string,

 

 

Hello World!

will display at the console.

Code Discussion

In the preceding example, the default marshaling for the parameter to the puts function has been overridden from the default of LPTSTR to LPSTR.

The MarshalAs attribute can be placed on method parameters, method return values, and fields of structs and classes. To set the marshaling of a method return value, place the MarshalAs attribute in an attribute block on the method with the return attribute location override. For example, to explicitly set the marshaling for the return value of theputs method:

 

 

...
[DllImport("msvcrt.dll")]
[return : MarshalAs(UnmanagedType.I4)]
public static extern int puts(
...

For more information on the syntax of the MarshalAs attribute, see MarshalAsAttribute Class.

Note   The In and Out attributes can be used to annotate parameters to unmanaged methods. They behave in a similar manner to the in and out modifiers in MIDL source files. Note that the Out attribute is different from the C# parameter modifier, out. For more information on the In and Out attributes, see InAttribute Class and OutAttribute Class.

Specifying Custom Marshaling for User-Defined Structs

You can specify custom marshaling attributes for fields of structs and classes passed to or from unmanaged functions. You do this by adding MarshalAs attributes to the fields of the struct or class. You must also use the StructLayout attribute to set the layout of the struct, optionally to control the default marshaling of string members, and to set the default packing size.

Example 3

This example demonstrates how to specify custom marshaling attributes for a struct.

Consider the following C structure:

 

 

typedef struct tagLOGFONT
{
   LONG lfHeight;
   LONG lfWidth;
   LONG lfEscapement;
   LONG lfOrientation;
   LONG lfWeight;
   BYTE lfItalic;
   BYTE lfUnderline;
   BYTE lfStrikeOut;
   BYTE lfCharSet;
   BYTE lfOutPrecision;
   BYTE lfClipPrecision;
   BYTE lfQuality;
   BYTE lfPitchAndFamily;
   TCHAR lfFaceName[LF_FACESIZE];
} LOGFONT;

In C#, you can describe the preceding struct by using the StructLayout and MarshalAs attributes as follows:

 

 

// logfont.cs
// compile with: /target:module
using System;
using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential)]
public class LOGFONT
{
    public const int LF_FACESIZE = 32;
    public int lfHeight;
    public int lfWidth;
    public int lfEscapement;
    public int lfOrientation;
    public int lfWeight;
    public byte lfItalic;
    public byte lfUnderline;
    public byte lfStrikeOut;
    public byte lfCharSet;
    public byte lfOutPrecision;
    public byte lfClipPrecision;
    public byte lfQuality;
    public byte lfPitchAndFamily;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=LF_FACESIZE)]
    public string lfFaceName;
}

For more information on the syntax of the StructLayout attribute, see StructLayoutAttribute Class.

The structure can then be used in C# code as shown below:

 

 

// pinvoke.cs
// compile with: /addmodule:logfont.netmodule
using System;
using System.Runtime.InteropServices;

class PlatformInvokeTest
{
      [DllImport("gdi32.dll", CharSet=CharSet.Auto)]
      public static extern IntPtr CreateFontIndirect(
            [In, MarshalAs(UnmanagedType.LPStruct)]
            LOGFONT lplf   // characteristics
            );

      [DllImport("gdi32.dll")]
      public static extern bool DeleteObject(
            IntPtr handle
            );

      public static void Main()
      {
            LOGFONT lf = new LOGFONT();
            lf.lfHeight = 9;
            lf.lfFaceName = "Arial";
            IntPtr handle = CreateFontIndirect(lf);

            if (IntPtr.Zero == handle)
            {
                  Console.WriteLine("Can't creates a logical font.");
            }
            else
            {

                  if (IntPtr.Size == 4)
                        Console.WriteLine("{0:X}", handle.ToInt32());
                  else
                        Console.WriteLine("{0:X}", handle.ToInt64());         

                  // Delete the logical font created.
                  if (!DeleteObject(handle))
                       Console.WriteLine("Can't delete the logical font");
            }
      }
}

Sample Run

 

 

C30A0AE5

Code Discussion

In the preceding example, the CreateFontIndirect method is using a parameter of the type LOGFONT. The MarshalAs and In attributes are used to qualify the parameter. The program displays the numeric value returned by the method as a hexadecimal uppercase string.

Registering Callback Methods

To register a managed callback that calls an unmanaged function, declare a delegate with the same argument list and pass an instance of it via PInvoke. On the unmanaged side it will appear as a function pointer. For more information about PInvoke and callback, see A Closer Look at Platform Invoke.

For example, consider the following unmanaged function, MyFunction, which requires callback as one of the arguments:

 

 

typedef void (__stdcall *PFN_MYCALLBACK)();
int __stdcall MyFunction(PFN_ MYCALLBACK callback);

To call MyFunction from managed code, declare the delegate, attach DllImport to the function declaration, and optionally marshal any parameters or the return value:

 

 

public delegate void MyCallback();
[DllImport("MYDLL.DLL")]
public static extern void MyFunction(MyCallback callback);

Also, make sure the lifetime of the delegate instance covers the lifetime of the unmanaged code; otherwise, the delegate will not be available after it is garbage-collected.

参考:http://msdn.microsoft.com/en-us/library/aa288468(v=vs.71).aspx