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qsort(3) — Linux manual page

qsort(3)                 Library Functions Manualqsort(3)

NAME        top

       qsort, qsort_r - sort an array

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#include <stdlib.h>void qsort(size_t n, size_t size;voidbase[n*size], size_tn, size_tsize,typeof(int (const void [size], const void [size]))*compar);void qsort_r(size_t n, size_t size;voidbase[n*size], size_tn, size_tsize,typeof(int (const void [size], const void [size], void *))*compar,void *arg);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):qsort_r():           _GNU_SOURCE

DESCRIPTION        top

       Theqsort() function sorts an array withn elements of sizesize.       Thebase 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 bycompar, 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       respectively less than, equal to, or greater than the second.  If       two members compare as equal, their order in the sorted array is       undefined.       Theqsort_r() function is identical toqsort() except that the       comparison functioncompar takes a third argument.  A pointer is       passed to the comparison function viaarg.  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        top

       Theqsort() andqsort_r() functions return no value.

ATTRIBUTES        top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────────────────┬───────────────┬─────────┐       │Interface│Attribute│Value│       ├──────────────────────────────────────┼───────────────┼─────────┤       │qsort(),qsort_r()                   │ Thread safety │ MT-Safe │       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS        top

qsort()              C11, POSIX.1-2008.

HISTORY        top

qsort()              POSIX.1-2001, C89, SVr4, 4.3BSD.qsort_r()              glibc 2.8.

NOTES        top

       To compare C strings, the comparison function can callstrcmp(3),       as shown in the example below.

EXAMPLES        top

       For one example of use, see the example underbsearch(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(*(const char **) p1, *(const char **) p2);       }       int       main(int argc, char *argv[])       {           if (argc < 2) {               fprintf(stderr, "Usage: %s <string>...\n", argv[0]);               exit(EXIT_FAILURE);           }           qsort(&argv[1], argc - 1, sizeof(char *), cmpstringp);           for (size_t j = 1; j < argc; j++)               puts(argv[j]);           exit(EXIT_SUCCESS);       }

SEE ALSO        top

sort(1),alphasort(3),strcmp(3),versionsort(3)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-06-28qsort(3)

Pages that refer to this page:bsearch(3), fts(3), scandir(3), tsearch(3)

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