C++/CLI剪辑

1.本地类中包含托管类成员变量的情况

 1 #include<vcclr.h>     // 必须包含vcclr.h头文件
 2 
 3 //传入
 4 
 5 A^ a = gcnew A();
 6 
 7 gcroot<A^> *pA = new gcroot<A^>();
 8 
 9 *pA = a;
10 
11 void *ptr = pA;
12 
13 B *b = new B(pA);  //c++类
14 
15 //还原
16 
17 gcroot<A^> *  m_pA = (gcroot<A^> *)pA；
18 
19 (*m_pA)->FuncA(); //可调用A类接口；

2.pin_ptr是防止您的对象移动将在垃圾回收堆的内部指针. 也就是说钉住指针的值不是由公共语言运行时更改. 当向非托管函数传递托管类的地址时，这很有用，因为在解析非托管函数调用的过程中，该地址不会意外更改.

pin_ptr无法使用情况(在pin_ptr的生命周期内有效)：

- 函数参数
- 作为函数的返回类型。
- 类成员的声明
- 目标的类型约束。

pin_ptr 数组的第一个元素的位置

 1 // pin_ptr_1.cpp  
 2 // compile with: /clr   
 3 using namespace System;  
 4 #define SIZE 10  
 5   
 6 #pragma unmanaged  
 7 // native function that initializes an array  
 8 void native_function(int* p) {  
 9    for(int i = 0 ; i < 10 ; i++)  
10     p[i] = i;  
11 }  
12 #pragma managed  
13   
14 public ref class A {  
15 private:  
16    array<int>^ arr;   // CLR integer array  
17   
18 public:  
19    A() {  
20       arr = gcnew array<int>(SIZE);  
21    }  
22   
23    void load() {  
24    pin_ptr<int> p = &arr[0];   // pin pointer to first element in arr  
25    int* np = p;   // pointer to the first element in arr  
26    native_function(np);   // pass pointer to native function  
27    }  
28   
29    int sum() {  
30       int total = 0;  
31       for (int i = 0 ; i < SIZE ; i++)  
32          total += arr[i];  
33       return total;  
34    }  
35 };  
36   
37 int main() {  
38    A^ a = gcnew A;  
39    a->load();   // initialize managed array using the native function  
40    Console::WriteLine(a->sum());  
41 }

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内部指针转换为钉住的指针，并且，类型为返回 address-of 运算符 (&) 是内部指针，当操作数在托管堆时

 1 // pin_ptr_2.cpp  
 2 // compile with: /clr  
 3 using namespace System;  
 4   
 5 ref struct G {  
 6    G() : i(1) {}  
 7    int i;  
 8 };  
 9   
10 ref struct H {  
11    H() : j(2) {}  
12    int j;  
13 };  
14   
15 int main() {  
16    G ^ g = gcnew G;   // g is a whole reference object pointer  
17    H ^ h = gcnew H;  
18   
19    interior_ptr<int> l = &(g->i);   // l is interior pointer  
20   
21    pin_ptr<int> k = &(h->j);   // k is a pinning interior pointer  
22   
23    k = l;   // ok  
24    Console::WriteLine(*k);  
25 };

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钉住的指针转换为另一种类型

 1 // pin_ptr_3.cpp  
 2 // compile with: /clr  
 3 using namespace System;  
 4   
 5 ref class ManagedType {  
 6 public:  
 7    int i;  
 8 };  
 9   
10 int main() {  
11    ManagedType ^mt = gcnew ManagedType;  
12    pin_ptr< int > pt = &mt->i;  
13    *pt = 8;  
14    Console::WriteLine(mt->i);  
15   
16    char *pc = ( char* ) pt;  
17    *pc = 255;  
18    Console::WriteLine(mt->i);  
19 }

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3.char * to array<unsigned char^>

 1 #pragma unmanaged
 2 
 3 void work_with_native_buffer(char* pBuffer, size_t size) {
 4     // Do your unmanaged stuff here
 5 }
 6 
 7 #pragma managed
 8 
 9 ref class Test {
10 public:
11     void DoNativeStuff() {
12         if (_buffer == nullptr)
13             _buffer = gcnew array<unsigned char>(256);
14 
15         pin_ptr<int> pinnedBuffer = &_buffer[0];
16         char* pBuffer = pinnedBuffer;
17         work_with_native_buffer(pBuffer, _buffer->Length);
18     }
19 
20     void SendData(Stream^ stream) {
21         Debug.Assert(_buffer != nullptr);
22 
23         stream->Write(_buffer, 0, _buffer->Length);
24     }
25 
26 private:
27     array<unsigned char>^ _buffer;
28 };

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使用 C++/CLI (Visual C++) 进行 .NET 编程