# qsort

## NAME



           qsort, qsort_r - sort an array
    


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## SYNOPSIS



           **#include <stdlib.h>**
    
           **void qsort(** size_t n, size_t size;
                      **void** _base_**[**_n_ *****_size_**], size_t** _n_**, size_t** _size_**,**
                      **typeof(int (const void [**_size_**], const void [**_size_**]))**
                          *****_compar_**);**
           **void qsort_r(** size_t n, size_t size;
                      **void** _base_**[**_n_ *****_size_**], size_t** _n_**, size_t** _size_**,**
                      **typeof(int (const void [**_size_**], const void [**_size_**], void *))**
                          *****_compar_**,**
                      **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 _n_ 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
           respectively 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.
    


## ATTRIBUTES



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


## STANDARDS



           **qsort**()
                  C11, POSIX.1-2008.
    


## NOTES



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


## EXAMPLES



           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(*(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);
           }
    


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