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man:qsort_r

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 compari-
     son 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.

ATTRIBUTES

     For   an   explanation   of   the  terms  used  in  this  section,  see
     attributes(7).
     allbox; lbw18 lb lb  l  l  l.   Interface Attribute Value  T{  qsort(),
     qsort_r() T}   Thread safety  MT-Safe

CONFORMING TO

     qsort(): POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES

     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>...\n", 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 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.
                                2017-09-15                          QSORT(3)
/data/webs/external/dokuwiki/data/pages/man/qsort_r.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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