90 lines
2.9 KiB
Markdown
90 lines
2.9 KiB
Markdown
# Circular Buffer
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A circular buffer, cyclic buffer or ring buffer is a data structure that
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uses a single, fixed-size buffer as if it were connected end-to-end.
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A circular buffer first starts empty and of some predefined length. For
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example, this is a 7-element buffer:
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[ ][ ][ ][ ][ ][ ][ ]
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Assume that a 1 is written into the middle of the buffer (exact starting
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location does not matter in a circular buffer):
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[ ][ ][ ][1][ ][ ][ ]
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Then assume that two more elements are added — 2 & 3 — which get
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appended after the 1:
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[ ][ ][ ][1][2][3][ ]
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If two elements are then removed from the buffer, the oldest values
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inside the buffer are removed. The two elements removed, in this case,
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are 1 & 2, leaving the buffer with just a 3:
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[ ][ ][ ][ ][ ][3][ ]
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If the buffer has 7 elements then it is completely full:
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[6][7][8][9][3][4][5]
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When the buffer is full an error will be raised, alerting the client
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that further writes are blocked until a slot becomes free.
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When the buffer is full, the client can opt to overwrite the oldest
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data with a forced write. In this case, two more elements — A & B —
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are added and they overwrite the 3 & 4:
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[6][7][8][9][A][B][5]
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3 & 4 have been replaced by A & B making 5 now the oldest data in the
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buffer. Finally, if two elements are removed then what would be
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returned is 5 & 6 yielding the buffer:
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[ ][7][8][9][A][B][ ]
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Because there is space available, if the client again uses overwrite
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to store C & D then the space where 5 & 6 were stored previously will
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be used not the location of 7 & 8. 7 is still the oldest element and
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the buffer is once again full.
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[D][7][8][9][A][B][C]
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## Getting Started
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Make sure you have read the "Guides" section of the
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[C track][c-track] on the Exercism site. This covers
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the basic information on setting up the development environment expected
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by the exercises.
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## Passing the Tests
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Get the first test compiling, linking and passing by following the [three
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rules of test-driven development][3-tdd-rules].
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The included makefile can be used to create and run the tests using the `test`
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task.
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make test
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Create just the functions you need to satisfy any compiler errors and get the
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test to fail. Then write just enough code to get the test to pass. Once you've
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done that, move onto the next test.
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As you progress through the tests, take the time to refactor your
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implementation for readability and expressiveness and then go on to the next
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test.
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Try to use standard C99 facilities in preference to writing your own
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low-level algorithms or facilities by hand.
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## Source
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Wikipedia [http://en.wikipedia.org/wiki/Circular_buffer](http://en.wikipedia.org/wiki/Circular_buffer)
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## Submitting Incomplete Solutions
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It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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[c-track]: https://exercism.io/my/tracks/c
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[3-tdd-rules]: http://butunclebob.com/ArticleS.UncleBob.TheThreeRulesOfTdd
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