lpNumberOfBytes

lpNumberOfBytes is a parameter used in various Windows API functions, particularly those dealing with memory management and data transfer. It typically represents a pointer to a DWORD variable that will receive the number of bytes read or written by the function. When a function is called with lpNumberOfBytes, the caller allocates a DWORD variable and passes its address. Upon successful completion of the function, the value stored in that DWORD variable is updated to reflect the actual number of bytes that were processed. This is crucial for operations like file I/O, network communication, or copying data between buffers, where the exact quantity of data handled might vary. It allows the calling application to determine how much data was successfully transferred, which is essential for subsequent processing or error handling. For instance, if a read operation is expected to retrieve a certain amount of data but returns fewer bytes, the lpNumberOfBytes parameter will indicate this discrepancy.