Buffers

Buffers
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Motivation

Stream:
- An infinitely long sequence of bytes that can be read from and/or written to
Buffer:
- A fixed amount of data that can be sent to or received from an I/O component

Properties

Properties (cont.)

Invariants:
- \(0 \leq \text{mark} \leq \text{position} \leq \text{limit} \leq \text{capacity}\)
Initial Values:
- \(\text{capacity} = \text{limit}\): Determined at construction-time
- position: 0
- mark: undefined

Operations on these Properties

Clear:
- Set the position to 0, the limit to the capacity, and discard the mark
Flip:
- Set the limit to the position, set the position to 0, and discard the mark if it is defined
Mark:
- Set the mark to the position
Reset:
- Set the position to the mark (leaving the mark unchanged)
Rewind:
- Set the position to 0, and discard the mark

Operations on the Contents

Filling:
- Puts a value into the element with index position and increases position (if limit hasn't been exceeded)
Draining:
- Gets the value from the element at index position and increases position (if limit hasn't been reached)

Operations on the Contents (cont.)

Putting It All Together

An Example