![]() | LowLevelReadString |
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;
[out] String read from the device.
[in] Number of bytes to read from the device.
[in] I/O timeout value in milliseconds.
Returns S_OK if successful, otherwise a failure HRESULT.
Unlike the buffered I/O functions, such as Queryf, ReadReadNumber, etc., the LowLevelReadString function reads raw bytes directly from the device, rather than going through formatted I/O read buffer.
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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. |
The following example demonstrates use of the LowLevelReadString function.
// 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.LowLevelReadString(pbstrName, 50); return hr; }