Knowledge Base Nr: 00046 memory_mapped_files.cpp - http://www.swe-kaiser.de

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Win32: beispiel für memory mapped files unter win nt

  
/////////////////////////////////////
typedef struct  //diesen struct anpassen
{
  short nVal1;
  short nVal2;
} MMFPARAM, *LPMMFPARAM;

int InitMMFData();     //initialisieren des memory mapped files (bei programmstart)
int CleanupMMFData();  //freigeben des memory mapped files      (bei programmende)
int ReadWriteMMFData(LPMMFPARAM lpMMFPARAM, bool bWrite);     //(zugriff auf den struct)

//diese funktionen sind auf den struct zugeschnitten!
short ReadDIOValue();
short WriteDIOValue(short nValue);

/////////////////////////////////////
HANDLE g_hFileMap = NULL;

int InitMMFData()
{
  if (g_hFileMap == NULL) //noch nicht offen
  {
    g_hFileMap = CreateFileMapping((HANDLE)0xffffffff,
                                    NULL,
                                    PAGE_READWRITE,
                                    0,
                                    sizeof(MMFPARAM),
                                    _T("DIOMemoryMappedFile"));

    if (g_hFileMap == NULL)
      return ::GetLastError();
  }

  if (GetLastError() == ERROR_ALREADY_EXISTS)
  {
    //file existiert bereits -> es kann z.b. gelesen werden
  }

  return 0;
}

int CleanupMMFData()
{
  if (g_hFileMap != NULL) //nur wenn offen
  {
    BOOL bSucc = ::CloseHandle(g_hFileMap);
    if (!bSucc)
      return ::GetLastError();
  }

  return 0;
}

int ReadWriteMMFData(LPMMFPARAM lpMMFPARAM, bool bWrite)
{
  InitMMFData(); //wenn schon initialisiert kehrt die funktion sofort zurück

  if (g_hFileMap == NULL)
    return -4711;

  LPVOID lpView = MapViewOfFile(g_hFileMap,
                                FILE_MAP_READ | FILE_MAP_WRITE,
                                0,
                                0,
                                0);

  if (lpView == NULL)
  {
    CleanupMMFData();
    return ::GetLastError();
  }

  LPMMFPARAM lpMMFPARAMFile = (LPMMFPARAM) lpView;

  if (bWrite) //schreiben
    memcpy(lpMMFPARAMFile, lpMMFPARAM, sizeof(LPMMFPARAM));
  else        //lesen
    memcpy(lpMMFPARAM, lpMMFPARAMFile, sizeof(LPMMFPARAM));

  BOOL bSucc = UnmapViewOfFile(lpView);
  if (!bSucc)
  {
    CleanupMMFData();
    return ::GetLastError();
  }

  return 0;
}

/////////////////////////////////////
//beispielfunktionen abhängig vom definierten struct
short ReadDIOValue()
{
  MMFPARAM sMMFPARAM;

  int nRes = ReadWriteMMFData(&sMMFPARAM, false);

  return sMMFPARAM.nVal1;
}

short WriteDIOValue(short nValue)
{
  MMFPARAM sMMFPARAM;

  sMMFPARAM.nVal1 = nValue;

  int nRes = ReadWriteMMFData(&sMMFPARAM, true);

  return sMMFPARAM.nVal1;
}

/////////////////////////////////////
//beispielnutzung

void CSharememDlg::OnLesen()
{
  short nValue = ReadDIOValue();

  CString str;
  str.Format("%d", nValue);
  GetDlgItem(IDC_VAL)->SetWindowText(str);
}

void CSharememDlg::OnSchreiben()
{
  CString str;
  GetDlgItem(IDC_VAL)->GetWindowText(str);
  short nValue = atoi(str);

  WriteDIOValue(nValue);
}