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qsort_s(3c)
qsort(3C) Standard C Library Functions qsort(3C)
NAME
qsort, qsort_r, qsort_s - quick sort
SYNOPSIS
#include <stdlib.h>
void qsort(void *base, size_t nel, size_t width,
int (*compar)(const void *x, const void *y));
void qsort_r(void *base, size_t nel, size_t width,
int (*compar)(const void *x, const void *y, void *context),
void *context);
#define __STDC_WANT_LIB_EXT1__ 1
#include <stdlib.h>
errno_t qsort_s(void *base, rsize_t nel, rsize_t width,
int (*compar)(const void *x, const void *y, void *context),
void *context);
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.
The qsort_r() function performs the same operation as the qsort() func‐
tion, differing in the addition of the context argument, which may hold
a user-defined value. This value is passed without interpretation to
the comparison function, and can be used to pass information between
the caller and the comparison function.
The qsort_s() function is part of the C11 bounds checking interfaces
specified in the C11 standard, Annex K. It is similar to the qsort()
function, but with differing parameters and return type and explicit
runtime-constraints as defined in the C11 standard. See runtime_con‐
straint_handler(3C) and INCITS/ISO/IEC 9899:2011.
RETURN VALUES
If no runtime-constraint violation is detected, qsort_s() returns zero,
otherwise, it returns a non-zero value.
ERRORS
The qsort(), qsort_r(), and qsort_s() functions will fail if:
EINVAL Null pointer is passed.
ERANGE size argument is not a valid value.
USAGE
The qsort() and qsort_r() functions safely allow concurrent access by
multiple threads to disjoint data, such as overlapping subtrees or ta‐
bles.
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);
return (i > j)
}
int
main()
{
int a[10] = { 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 };
size_t nelems = sizeof (a) / sizeof (int);
qsort(a, nelems, sizeof (int), intcompare);
for (size_t i = 0; i < nelems; i++) {
(void) printf("%d ", a[i]);
}
(void) printf("\n");
return (0);
}
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelSee below _
StandardSee standards(7).
The qsort() and qsort_r() functions can be used safely in multithreaded
applications.
The qsort_s() function cannot be used safely in a multithreaded appli‐
cation due to the runtime constraint handler. For more information, see
the runtime_constraint_handler(3C) man page.
SEE ALSO
sort(1), bsearch(3C), bsearch_s(3C), lsearch(3C), strcmp(3C),
strxfrm(3C), attributes(7), standards(7),
runtime_constraint_handler(3C)
NOTES
The comparison function need not compare every byte, so arbitrary data
may be contained in the elements in addition to the values being com‐
pared.
The relative order in the output of two items that compare as equal is
unpredictable.
Historically, global variables have been used with the qsort() function
to pass additional data from the caller to the comparison function. The
qsort_r() function provides a reentrant mechanism for sharing such
data, avoiding the need for global data, and is preferred in such situ‐
ations.
HISTORY
The qsort_r() function was added in Oracle Solaris 11.4.12.
The qsort_s() function was added in Oracle Solaris 11.4.0.
The qsort() function has been included in all Sun and Oracle releases
of Solaris.
Oracle Solaris 11.4 27 Oct 2025 qsort(3C)