C++使用共享内存实现进程间通信

C++使用共享内存实现进程间通信
文件映射是一种实现进程间单向或双向通信的机制。它允许两个或多个本地进程间相互通信。为了共享文件或内存，所有的进程必须使用相同的文件映射的名字或是句柄。
为了实现共享文件，第一个进程先调用CreateFile方法。接下来调用CreateFileMapping方法来创建一个文件映射对象。并为文件映射指明一个句柄和名称。由于事件，信号，互斥对象和文件映射等这些内核对象都共享同一个名字空间，所以如果这个名字和其他一个对象的名称重名的话那么将创建失败。
为了实现共享内存，进程应首先调用CreateFileMapping函数然后在hFile参数中传入INVALID_HANDLE_VALUE宏来替代句柄。相应的文件映射对象会从系统的分页文件中获得一段内存。如果hFile参数的值是INVALID_HANDLE_VALUE，那么你在调用CreateFileMapping时必须给共享内存指定一个大小值。
使用共享内存或文件的进程必须使用MapViewOfFile函数或MapViewOfFileEx函数来创建一个文件视图。
下面我们创建一个名称为"Local\SampleMap"的文件映射对象，并将一个字符串写入到文件映射中。
我们将创建两个程序，一个是服务程序，一个是客户程序。服务程序负责创建文件映射。
服务程序命名为CppFileMappingServer，它的执行过程是
1.创建一个特定大小的文件映射对象，名称为“Local\SampleMap”
2.将这个对象的文件视图映射到进程的地址空间，然后向视图中写入字符串。

接下来执行客户程序CppFileMappingClient，它首先打开这个名称为“Local\SampleMap”的文件映射对象。然后把相同的文件映射视图映射到自己的地址空间中。然后从视图中读取服务进程所写入的数据。

Server完整源码：

#pragma region Includes  
#include <stdio.h>  
#include <windows.h>  
#pragma endregion  
#define MAP_PREFIX          L"Local\\"  
#define MAP_NAME            L"SampleMap"  
#define FULL_MAP_NAME       MAP_PREFIX MAP_NAME  
  
// Max size of the file mapping object.  
#define MAP_SIZE            65536  
  
// File offset where the view is to begin.  
#define VIEW_OFFSET         0  
  
// The number of bytes of a file mapping to map to the view. All bytes of the   
// view must be within the maximum size of the file mapping object (MAP_SIZE).   
// If VIEW_SIZE is 0, the mapping extends from the offset (VIEW_OFFSET) to    
// the end of the file mapping.  
#define VIEW_SIZE           1024  
  
// Unicode string message to be written to the mapped view. Its size in byte   
// must be less than the view size (VIEW_SIZE).  
#define MESSAGE             L"Message from the first process."  
  
  
int wmain(int argc, wchar_t* argv[])  
{  
    HANDLE hMapFile = NULL;  
    PVOID pView = NULL;  
  
    // Create the file mapping object.  
    hMapFile = CreateFileMapping(  
        INVALID_HANDLE_VALUE,   // Use paging file - shared memory  
        NULL,                   // Default security attributes  
        PAGE_READWRITE,         // Allow read and write access  
        0,                      // High-order DWORD of file mapping max size  
        MAP_SIZE,               // Low-order DWORD of file mapping max size  
        FULL_MAP_NAME           // Name of the file mapping object  
        );  
    if (hMapFile == NULL)   
    {  
        wprintf(L"CreateFileMapping failed w/err 0x%08lx\n", GetLastError());  
        goto Cleanup;  
    }  
    wprintf(L"The file mapping (%s) is created\n", FULL_MAP_NAME);  
  
    // Map a view of the file mapping into the address space of the current   
    // process.  
    pView = MapViewOfFile(  
        hMapFile,               // Handle of the map object  
        FILE_MAP_ALL_ACCESS,    // Read and write access  
        0,                      // High-order DWORD of the file offset   
        VIEW_OFFSET,            // Low-order DWORD of the file offset   
        VIEW_SIZE               // The number of bytes to map to view  
        );  
    if (pView == NULL)  
    {   
        wprintf(L"MapViewOfFile failed w/err 0x%08lx\n", GetLastError());   
        goto Cleanup;  
    }  
    wprintf(L"The file view is mapped\n");  
  
    // Prepare a message to be written to the view.  
    PWSTR pszMessage = MESSAGE;  
    DWORD cbMessage = (wcslen(pszMessage) + 1) * sizeof(*pszMessage);  
  
    // Write the message to the view.  
    memcpy_s(pView, VIEW_SIZE, pszMessage, cbMessage);  
  
    wprintf(L"This message is written to the view:\n\"%s\"\n",  
        pszMessage);  
  
    // Wait to clean up resources and stop the process.  
    wprintf(L"Press ENTER to clean up resources and quit");  
    getchar();  
  
Cleanup:  
  
    if (hMapFile)  
    {  
        if (pView)  
        {  
            // Unmap the file view.  
            UnmapViewOfFile(pView);  
            pView = NULL;  
        }  
        // Close the file mapping object.  
        CloseHandle(hMapFile);  
        hMapFile = NULL;  
    }  
  
    return 0;  
}  

Client完整源码

#pragma region Includes  
#include <stdio.h>  
#include <windows.h>  
#pragma endregion  
#define MAP_PREFIX          L"Local\\"  
#define MAP_NAME            L"SampleMap"  
#define FULL_MAP_NAME       MAP_PREFIX MAP_NAME  
  
// File offset where the view is to begin.  
#define VIEW_OFFSET         0  
  
// The number of bytes of a file mapping to map to the view. All bytes of the   
// view must be within the maximum size of the file mapping object. If   
// VIEW_SIZE is 0, the mapping extends from the offset (VIEW_OFFSET) to the   
// end of the file mapping.  
#define VIEW_SIZE           1024  
  
  
int wmain(int argc, wchar_t* argv[])  
{  
    HANDLE hMapFile = NULL;  
    PVOID pView = NULL;  
  
    // Try to open the named file mapping identified by the map name.  
    hMapFile = OpenFileMapping(  
        FILE_MAP_READ,          // Read access  
        FALSE,                  // Do not inherit the name  
        FULL_MAP_NAME           // File mapping name   
        );  
    if (hMapFile == NULL)   
    {  
        wprintf(L"OpenFileMapping failed w/err 0x%08lx\n", GetLastError());  
        goto Cleanup;  
    }  
    wprintf(L"The file mapping (%s) is opened\n", FULL_MAP_NAME);  
  
    // Map a view of the file mapping into the address space of the current   
    // process.  
    pView = MapViewOfFile(  
        hMapFile,               // Handle of the map object  
        FILE_MAP_READ,          // Read access  
        0,                      // High-order DWORD of the file offset   
        VIEW_OFFSET,            // Low-order DWORD of the file offset  
        VIEW_SIZE               // The number of bytes to map to view  
        );  
    if (pView == NULL)  
    {  
        wprintf(L"MapViewOfFile failed w/err 0x%08lx\n", GetLastError());   
        goto Cleanup;  
    }  
    wprintf(L"The file view is mapped\n");  
  
    // Read and display the content in view.  
    wprintf(L"Read from the file mapping:\n\"%s\"\n", (PWSTR)pView);  
  
    // Wait to clean up resources and stop the process.  
    wprintf(L"Press ENTER to clean up resources and quit");  
    getchar();  
  
Cleanup:  
  
    if (hMapFile)  
    {  
        if (pView)  
        {  
            // Unmap the file view.  
            UnmapViewOfFile(pView);  
            pView = NULL;  
        }  
        // Close the file mapping object.  
        CloseHandle(hMapFile);  
        hMapFile = NULL;  
    }  
  
    return 0;  
}  

运行效果：

Server

Client