c#编程指南(十一)平台调用P-INVOKE完全掌握,指针大全

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这篇是讲述P-INVOKE中，应对各种指针的方法。包括普通指针，字符串指针，二级指针，指针数组，函数指针，结构体指针。篇幅估计有点长，大家耐心点看。嘿嘿~~

第一：普通指针，包括char *,short *,int *,__int64 *,这些指针进行平台调用是都对应C#的IntPtr类型,然后使用Marshal.ReadXXX()系列函数读取就可，写内存时使用Marshal.WriteXXX()系列函数就行。

c++:



28  static int test5 = 100;
29  int * __stdcall ReadInt()
30 {
31     return &test5;
32 }

c#:注意Marshal.ReadXXX()系列函数的使用



15         [DllImport("TestDll")]
16         public static extern IntPtr ReadInt();
29         //##############################
42             IntPtr p5 = ReadInt();
43             Console.WriteLine(Marshal.ReadInt32(p5));
44             IntPtr p6 = ReadUint();
45             Console.WriteLine(Convert.ToUInt32(Marshal.ReadInt32(p6)));

第二：字符串指针上一篇已经有过讨论，可以使用marshalAs返回值，当然也可以用Marshal.PtrToStringAuto()来读取字符串。个人推荐第一个。

c++:


 1 static char * test9 = "you are very very bad bad girl, gaga!";
 2  char * __stdcall ReadString()
 3 {
 4     return test9;
 5 }
 6 
 7 
 8  static wchar_t * test10 = TEXT("you are very very bad bad girl, gaga!");
 9 wchar_t  * __stdcall ReadStringW()
10 {
11     return test10;
12 }

c#:注意Marshal.PtrToStringAuto（）函数的使用。


 1         [DllImport("TestDll")]
 2         [return: MarshalAs(UnmanagedType.LPStr)]
 3         public static extern string ReadString();
 4 
 5         [DllImport("TestDll")]
 6         public static extern IntPtr ReadStringW();
 7             //#########################
 8             Console.WriteLine(ReadString());
 9 
10             IntPtr p9 = ReadStringW();
11             Console.WriteLine(Marshal.PtrToStringAuto(p9));

第三：函数指针，C#的委托就对应C++的__stdcall调用协议的函数指针。前面也有讨论。

c++:


1 typedef void (__stdcall * FunctionPoint)(void);
2 void __stdcall TestFunction(){printf("you are very very bad bad girl, gaga!\n");}
3 FunctionPoint __stdcall GetFunctionPointer()
4 {
5     return TestFunction;
6 }

c#:


1         public delegate void FunctionPointer();
2         [DllImport("TestDll")]
3         public static extern FunctionPointer GetFunctionPointer();
4             //#########################
5             FunctionPointer pointer = GetFunctionPointer();
6             pointer();

第四：指针的指针，也就是二级指针，要使用Marshal.ReadIntPtr(）来读取。

c++:


1 static int test11 = 555;
2 static int * test12 = &test11;
3 int ** __stdcall ReadPoint2()
4 {
5     return &test12;
6 }

c#:


1         [DllImport("TestDll")]
2         public static extern IntPtr ReadPoint2();
3             //#########################
4             IntPtr p10 = ReadPoint2();
5             IntPtr p11 = Marshal.ReadIntPtr(p10);
6             int test10 = Marshal.ReadInt32(p11);
7             Console.WriteLine(test10);

第五：指针数组没有太直接的方法，因为C++所有指针都是4BYTE所以这里我是这么读的。

C++:


 1 static int test13 = 666;
 2 static int test14 = 777;
 3 static int * test15[3] = {0};
 4 int **  __stdcall ReadPointArray()
 5 {
 6     test15[0] = &test11;
 7     test15[1] = &test13;
 8     test15[2] = &test14;
 9     return test15;
10 }

C#:


1         [DllImport("TestDll")]
2         public static extern IntPtr ReadPointArray();            
3 //#########################
4             IntPtr p12 = ReadPointArray();
5             int test11 = p12.ToInt32();
6             Console.WriteLine(Marshal.ReadInt32(Marshal.ReadIntPtr(p12)));
7             Console.WriteLine(Marshal.ReadInt32(Marshal.ReadIntPtr(new IntPtr(test11 + 0))));
8             Console.WriteLine(Marshal.ReadInt32(Marshal.ReadIntPtr(new IntPtr(test11 + 4))));
9             Console.WriteLine(Marshal.ReadInt32(Marshal.ReadIntPtr(new IntPtr(test11 + 8))));

最后: 结构体的指针，用C#建立对应C++的结构体，并使用 [StructLayout(LayoutKind.Sequential)]属性，

使用Marshal.PtrToStructure()读取。

c++:


 1 struct Test
 2 {
 3     int test;
 4 };
 5 
 6 static Test test16;
 7 Test * __stdcall ReadStruct()
 8 {
 9     test16.test = 1234;
10     return &test16;
11 }

c#:


 1         [StructLayout(LayoutKind.Sequential)]
 2         public struct Test
 3         {
 4             public int test;
 5         }
 6 
 7         [DllImport("TestDll")]
 8         public static extern IntPtr ReadStruct();
 9             //#########################
10 
11             IntPtr p13 = ReadStruct();
12             Test test13 = (Test)Marshal.PtrToStructure(p13,typeof(Test));
13             Console.WriteLine(test13.test);