cbOutBuffer

cbOutBuffer is a variable name commonly used in low-level I/O and driver development to denote the size or length of an output buffer in a call that transfers data from a device, subsystem, or function back to the caller. The prefix “cb” is a common shorthand for “count of bytes,” so cbOutBuffer typically represents how many bytes the output buffer can hold or how many bytes were actually written to the buffer during the operation. The exact meaning can vary by API, codebase, or documentation.

In practice, cbOutBuffer appears in contexts such as device I/O control (IOCTL) paths, wrapper libraries, and sample drivers. It is often paired with a corresponding cbInBuffer, which denotes the size of any input data provided to the function. Depending on the interface, cbOutBuffer may indicate either:

- the allocated capacity of the output buffer supplied by the caller, or

- the number of bytes actually returned to the output buffer after the call completes.

The specific semantics are API-dependent. Some interfaces use cbOutBuffer purely as an input parameter describing the buffer size, while others use it as an output parameter or as part of a combined in/out protocol. Types for these variables are typically unsigned integers (such as size_t, DWORD, or ULONG) to represent byte counts and to enable size checks before performing transfers.

Because the precise meaning of cbOutBuffer can differ between APIs, developers should consult the relevant API or driver documentation to confirm whether it refers to buffer capacity, bytes transferred, or both in a given function or I/O control. See also cbInBuffer for the complementary concept of input data size.