The `qsort()` Library Function

The Standard C/C++ Library contains the function qsort() that performs a Quick Sort on an array.
Prototype void qsort(void* base, size_t nmemb, size_t size, int (*compar) (const void*, const void*)); where
- base is the address of the first element of the array.
- nmemb is the number of members in the array.
- size is the number of bytes in a single array element.
- compar() is a function that compares two array elements.
- compar() returns
  - a negative integer if the first element is less than the second element.
  - zero if the first element is equal to the second element.
  - a positive integer if the first element is greater than the second element.
The function compar() must define a total order on the objects in the class.
- For all objects a, b, c, the following properties hold:
  - Reflexivity: a <= a.
  - Anti-symmetry: If a <= b and b <= a, then a == b.
  - Transitivity: If a <= b and b <= c, then a <= c.
  - Trichotomy: Either a < b or a == b or a > b.

This page was last modified on Apr 23, 2001

URL: http://people.hsc.edu/faculty-staff/robbk/Coms262/Lectures/TheqsortFunction.html

The qsort() Library Function