What the DeviceIocontrol API function will do? - delphi

Question

Please explain what does this VC++ code do? Is it possible to convert this code to Delphi2010?
void CDMOnLineView::OnActionGetdata()
{
bool retCode;
DWORD retByte = 0;
int TmpHigh, TmpLow;
UCHAR HIDData[64];
int LastX, LastY;
UCHAR Button;
CDC* pViewDC = GetDC();
if(yPos > 500) yPos = 0;
else yPos = yPos + 16;
if(hDriver == NULL)
{
pViewDC->TextOut(10,yPos,"Driver not connect yet.");
}
else
{
IO_Param.CallerHandle = m_hWnd;
IO_Param.Model = DM_A4;
retCode = DeviceIoControl(hDriver, IOCTL_DM_READ_DATA, &IO_Param, sizeof(DM_PARAM), HIDData,
6, &retByte, NULL);
if(retCode)
{
if(retByte != 0)
{
Button = HIDData[1] & 0x01;
TmpLow = (int)HIDData[2];
TmpHigh = (int)HIDData[3];
LastX = (TmpLow & 0x00FF) | ((TmpHigh << 8) & 0xFF00);
TmpLow = (int)HIDData[4];
TmpHigh = (int)HIDData[5];
LastY = (TmpLow & 0x00FF) | ((TmpHigh << 8) & 0xFF00);
sprintf(szStringBuffer, "Button: %d, X: %.5d, Y: %.5d", Button, LastX, LastY);
pViewDC->TextOut(10,yPos,szStringBuffer, strlen(szStringBuffer));
}
else pViewDC->TextOut(10,yPos,"Return bytes incorrect.");
}
else
{
ErrorCode = GetLastError();
sprintf(szStringBuffer, "Call IOCTL_DM_READ_DATA fail. Error: %d", ErrorCode);
pViewDC->TextOut(10,yPos,szStringBuffer, strlen(szStringBuffer));
}
}
ReleaseDC(pViewDC);
}
What the DeviceIocontrol function will do? Please try to explain the parameters also.
thanks all.

Answer 1

Here's the "translation" of all those bitwise operations in the code, hopefully those would get you going:
The operators you need to know about:
& as the bitwise AND operator.
| is the bitwise OR operator
<< is the bitwise SHIFT LEFT operator
The translations:
Button = HIDData[1] & 0x01; // C
Button := HIDData[1] and $01; // Delphi
TmpLow = (int)HIDData[2]; // C
TmpLow := Integer(HIDData[2]); // Delphi
TmpHigh = (int)HIDData[3]; // C
TmpHigh := Integer(HidData[3]); // Delphi
LastX = (TmpLow & 0x00FF) | ((TmpHigh << 8) & 0xFF00); // C
LastX := (TmpLow and $00FF) or ((TmpHigh shl 8) and $FF00); // Delphi
TmpLow = (int)HIDData[4]; // C
TmpLow := Integer(HIDData[4]); // Delphi
TmpHigh = (int)HIDData[5]; // C
TmpHigh := Integer(HIDData[5]); // Delphi
LastY = (TmpLow & 0x00FF) | ((TmpHigh << 8) & 0xFF00); // C
LastY := (TmpLow and $00FF) or ((TmpHigh shl 8) and $FF00); // Delphi
sprintf(szStringBuffer, "Button: %d, X: %.5d, Y: %.5d", Button, LastX, LastY); // C
pViewDC->TextOut(10,yPos,szStringBuffer, strlen(szStringBuffer)); // C
Caption := Format('Button: %d, x: %.5d, y: %.5d', [Button, LastX, LastY]); // Delphi

Answer 2

DeviceIoControl calls custom driver function. Driver is kernel-mode program representing some computer device. Drivers have standard operations (like open, close, read, write, which are called using CreateFile, CloseHandle, ReadFile and WriteFile API) and custom driver-specific operations, called using DeviceIoControl. Details about these operations are described in the driver documentation.
Every custom operation has generic interface: operation code, input and output buffers, which may contain any information.

Answer 3

The DeviceIoControl function is documented at MSDN. User mode programs use it to interact with device drivers.
Converting this code is pretty simple. The call to DeviceIoControl maps across trivially. The only area that you are likely to struggle with is the C bitwise operations. If you don't have a copy of K&R to hand, then you should!