LowLevelReadStringNoPoll

Reads raw bytes directly from a device without going through the formatted I/O read buffer and returns the results as a string.

virtual HRESULT LowLevelReadString(CString& pBuf, long cchDesired, long lTimeout = CUR_TIMEOUT)  override;

virtual HRESULT LowLevelReadString(BSTR* pBuf, long cchDesired, long lTimeout = CUR_TIMEOUT) override;

Parameters

pBuf: [out] String read from the device.
cchDesired: [in] Number of bytes to 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 LowLevelReadString 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 LowLevelReadStringNoPoll function.

C++

Copy

// CoAcme4321.cpp
STDMETHODIMP Acme4321::IAcme4321_QueryName(BSTR* pbstrName)
{
  HRESULT hr = S_OK;

  // Read up to 50 bytes and return as a BSTR
  hr = io.LowLevel.LowLevelReadStringNoPoll(pbstrName, 50);

  return hr;
}

Other Resources

LowLevelRead

LowLevelReadNoPoll

LowLevelReadString