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qsort(3c) [opensolaris man page]

qsort(3C)						   Standard C Library Functions 						 qsort(3C)

NAME
qsort - quick sort SYNOPSIS
#include <stdlib.h> void qsort(void *base, size_t nel, size_t width, int (*compar)(const void *, const void *)); DESCRIPTION
The qsort() function is an implementation of the quick-sort algorithm. It sorts a table of data in place. The contents of the table are sorted in ascending order according to the user-supplied comparison function. The base argument points to the element at the base of the table. The nel argument is the number of elements in the table. The width argument specifies the size of each element in bytes. The compar argument is the name of the comparison function, which is called with two arguments that point to the elements being compared. The function must return an integer less than, equal to, or greater than zero to indicate if the first argument is to be considered less than, equal to, or greater than the second argument. The contents of the table are sorted in ascending order according to the user supplied comparison function. USAGE
The qsort() function safely allows concurrent access by multiple threads to disjoint data, such as overlapping subtrees or tables. EXAMPLES
Example 1 Program sorts. The following program sorts a simple array: #include <stdlib.h> #include <stdio.h> static int intcompare(const void *p1, const void *p2) { int i = *((int *)p1); int j = *((int *)p2); if (i > j) return(1); if (i < j) return (-1); return(0); } int main() { int i; int a[10] = { 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 }; size_t nelems = sizeof (a) / sizeof (int); qsort((void *)a, nelems, sizeof (int), intcompare); for (i = 0; i < nelems; i++) { (void) printf("%d ", a[i]); } (void) printf(" "); return(0); } ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
sort(1), bsearch(3C), lsearch(3C), string(3C), attributes(5), standards(5) NOTES
The comparison function need not compare every byte, so arbitrary data may be contained in the elements in addition to the values being compared. The relative order in the output of two items that compare as equal is unpredictable. SunOS 5.11 6 Dec 2004 qsort(3C)

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QSORT(3)						     Linux Programmer's Manual							  QSORT(3)

NAME
qsort, qsort_r - sort an array SYNOPSIS
#include <stdlib.h> void qsort(void *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *)); void qsort_r(void *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *, void *), void *arg); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): qsort_r(): _GNU_SOURCE DESCRIPTION
The qsort() function sorts an array with nmemb elements of size size. The base argument points to the start of the array. The contents of the array are sorted in ascending order according to a comparison function pointed to by compar, which is called with two arguments that point to the objects being compared. The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respec- tively less than, equal to, or greater than the second. If two members compare as equal, their order in the sorted array is undefined. The qsort_r() function is identical to qsort() except that the comparison function compar takes a third argument. A pointer is passed to the comparison function via arg. In this way, the comparison function does not need to use global variables to pass through arbitrary arguments, and is therefore reentrant and safe to use in threads. RETURN VALUE
The qsort() and qsort_r() functions return no value. VERSIONS
qsort_r() was added to glibc in version 2.8. CONFORMING TO
The qsort() function conforms to SVr4, 4.3BSD, C89, C99. NOTES
Library routines suitable for use as the compar argument to qsort() include alphasort(3) and versionsort(3). To compare C strings, the comparison function can call strcmp(3), as shown in the example below. EXAMPLE
For one example of use, see the example under bsearch(3). Another example is the following program, which sorts the strings given in its command-line arguments: #include <stdio.h> #include <stdlib.h> #include <string.h> static int cmpstringp(const void *p1, const void *p2) { /* The actual arguments to this function are "pointers to pointers to char", but strcmp(3) arguments are "pointers to char", hence the following cast plus dereference */ return strcmp(* (char * const *) p1, * (char * const *) p2); } int main(int argc, char *argv[]) { int j; if (argc < 2) { fprintf(stderr, "Usage: %s <string>... ", argv[0]); exit(EXIT_FAILURE); } qsort(&argv[1], argc - 1, sizeof(char *), cmpstringp); for (j = 1; j < argc; j++) puts(argv[j]); exit(EXIT_SUCCESS); } SEE ALSO
sort(1), alphasort(3), strcmp(3), versionsort(3) COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2012-03-08 QSORT(3)
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