NAME
qsort - sorts an array
SYNOPSIS
#include <stdlib.h>
I void qsort(void * base , size_t nmemb , size_t size ,
I int(* compar )(const void *, const void *));
DESCRIPTION
The
R 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 respectively
less than, equal to, or greater than the second.
If two members compare
as equal, their order in the sorted array is undefined.
RETURN VALUE
The
R qsort ()
function returns no value.
CONFORMING TO
SVr4, 4.3BSD, C89, C99.
NOTES
Library routines suitable for use as the
compar
argument 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 example program,
which sorts the strings given in its command-line arguments:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <assert.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;
assert(argc > 1);
qsort(&argv[1], argc - 1, sizeof(char *), cmpstringp);
for (j = 1; j < argc; j++)
puts(argv[j]);
exit(EXIT_SUCCESS);
}
SEE ALSO
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