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);
}