LowLevelReadNoPoll

Reads raw bytes directly from a device without going through the formatted I/O read buffer.

virtual HRESULT LowLevelReadNoPoll(BYTE* pBuf, long cbDesired, long* pcbActual, long lTimeout = CUR_TIMEOUT) override;

virtual HRESULT LowLevelReadNoPoll(SAFEARRAY** pBuf, long cbDesired, long lTimeout = CUR_TIMEOUT) override;

Parameters

pBuf: [out] Array of bytes read from the device.
cbDesired: [in] Number of bytes to read from the device.
pcbActual: [out] Actual number of bytes read from the device.
lTimeout: [in] I/O timeout value in milliseconds.

Return Value

Returns S_OK if successful, otherwise a failure HRESULT.

Remarks

This function behaves identically to the LowLevelRead function except that the device is not polled for errors after the data is read.

Caution
It is critical that these low-level functions not be intermixed with buffered I/O functions in a sequence of operations, such as a set of calls implementing a single driver method. The buffered I/O functions assume that all data read from or sent to the device passes through the I/O buffer, and intermixing these calls with low-level functions that directly access the device can produce incorrect results and/or I/O errors.

Caution

It is critical that these low-level functions not be intermixed with buffered I/O functions in a sequence of operations, such as a set of calls implementing a single driver method. The buffered I/O functions assume that all data read from or sent to the device passes through the I/O buffer, and intermixing these calls with low-level functions that directly access the device can produce incorrect results and/or I/O errors.

Example

The following example demonstrates use of the LowLevelReadNoPoll function.

C++

Copy

// CoAcme4321.cpp
STDMETHODIMP Acme4321::IAcme4321_QueryData(SAFEARRAY** ppsaData)
{
  HRESULT hr = S_OK;

  // Read 1000 bytes
  hr = io.LowLevel.LowLevelReadNoPoll(ppsaData, 1000);

  return hr;
}

Other Resources

LowLevelRead

LowLevelReadString

LowLevelReadStringNoPoll