Memory Mapped File

#include <string>

using namespace
std;

/**************************************************************************************************

       CMemMapFile

       Class to store a structure in a memory mapped file.

       The purpose for using a memory mapped file is to cross process boundaries.

       This simple class only has a constructor, destructor, and accessor.

       Use is as follows:

struct MyDataStruct        // this could also be “class MyDataStruct

{

       int x;

       int y;

}

SomeFunctionThatNeedsMemoryMappedData()

{

// create the data file

       CMemMapFile<MyDataStruct> myData(_T(“MyFunctionsMemoryMappedDataFile“));

// use the data file

       if(myData)

       {

              myData->x = 5;             // assign, which stores to mem mapped file

              myData->y = 5;

              cout << myData->x;         // access data (from mem mapped file)

              cout << myData->y;

       }

       else

              cout << “Construction of myData failed!!”

// destructor will get called when myData goes out of scope, and get rid of file

}

**************************************************************************************************/

 

template <class T>

class CMemMapFile

{

public:

       CMemMapFile(wstring Name);       // must construct with a name

       ~CMemMapFile();                 // destructor

       T* operator->() { return m_pData; }         // access data with pointer operator e.g. myData->x = 5;

       operator bool() { return m_hFile && m_pData; }  // test for validity e.g if(myData)…

private:

       HANDLE               m_hFile;

       T*                         m_pData;

};

 

template <class T>

CMemMapFile<T>::CMemMapFile(wstring Name)

{

       m_hFile = NULL;

       m_pData = NULL;

       if(Name.length() == 0) return;

       m_hFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, sizeof(T), Name.c_str());

       if (m_hFile)

       {

              m_pData = (T*) MapViewOfFile(m_hFile, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, 0);

              if (!m_pData)

                     CloseHandle(m_hFile);

       }

}

 

template <class T>

CMemMapFile<T>::~CMemMapFile()

{

       if(m_pData)

              UnmapViewOfFile(m_pData);

       if(m_hFile)

              CloseHandle(m_hFile);

}

 

 

 

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