Comparison function
A comparison function or strategy compares two values and indicates their relative ordering, and sometimes whether they are equivalent.
Clojure: The Essential Reference
The Java Comparator interface defines an object contract for comparing two values through a compare method.
- How it is used
- Orders values for sorting and for sorted maps and sets, with custom comparisons when default ordering is unsuitable.
- How deep it goes
- Defines the three-way result, works through custom ordering and tie-breakers, and identifies incompatible inputs and NaN behavior.
- Examples
- Uses reversed string ordering, equal-length vector collisions, and vector tie-breakers to demonstrate comparator behavior.
- What you can do after
- Apply it via sorted-map-by and sorted-set-by to choose an order without unintentionally collapsing distinct keys or elements.
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Modern C, Third Edition
A comparison function is a caller-supplied function that determines the ordering or equality of two data elements for an algorithm such as sorting or searching.
- How it is used
- Deploys comparison functions as callbacks that give qsort and bsearch an ordering for otherwise type-generic data.
- How deep it goes
- Explains the callback contract, void-pointer conversions, overflow hazard, and sortedness requirement without developing ordering theory further.
- Examples
- Uses unsigned comparison code, an invalid subtractive integer comparator, and qsort or bsearch interfaces.
- What you can do after
- Apply qsort and bsearch with comparison callbacks that preserve element types, ordering results, overflow safety, and sortedness.
Read how Modern C, Third Edition explains comparison function →
Modern C
A comparison function is a callback that determines the ordering of two values by returning a negative, zero, or positive result.
- How it is used
- Deploys callbacks to give qsort and bsearch type-independent ordering information for array elements.
- How deep it goes
- Explains the return contract, void-pointer conversions, and integer-overflow pitfall, but defers a complete search or sorting implementation.
- Examples
- Uses unsigned comparison code, an overflowing integer subtraction comparator, and qsort/bsearch declarations.
- What you can do after
- Apply it via qsort and bsearch by writing a consistent comparator and supplying the correct element size.
Related concepts
- qsortused by · qsort is a C standard-library function that sorts an array using a caller-supplied comparison function.
- bsearchused by · bsearch is a C standard-library function that performs a binary search on a sorted array using a caller-provided comparison function.
- sorting algorithmused by · A sorting algorithm is a procedure that rearranges elements of a collection into an order determined by an ordering criterion.
- sorted-map-byused by · sorted-map-by is a Clojure constructor function that creates a persistent map whose keys are ordered by a supplied comparator.
- sort-byused by · sort-by is a Clojure function that orders collection elements according to keys computed by a supplied function.
- callbackkind of · A callback is a function or other callable supplied to software for invocation later in response to a specified event, condition, or point in execution.
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