<s>
qsort	B-Language
is	O
a	O
C	B-Language
standard	I-Language
library	I-Language
function	O
that	O
implements	O
a	O
polymorphic	B-Application
sorting	B-Algorithm
algorithm	I-Algorithm
for	O
arrays	O
of	O
arbitrary	O
objects	O
according	O
to	O
a	O
user-provided	O
comparison	O
function	O
.	O
</s>
<s>
It	O
is	O
named	O
after	O
the	O
"	O
quicker	O
sort	O
"	O
algorithm	O
(	O
a	O
quicksort	B-Algorithm
variant	O
due	O
to	O
R	O
.	O
S	O
.	O
Scowen	O
)	O
,	O
which	O
was	O
originally	O
used	O
to	O
implement	O
it	O
in	O
the	O
Unix	B-Application
C	B-Language
library	I-Language
,	O
although	O
the	O
C	O
standard	O
does	O
not	O
require	O
it	O
to	O
implement	O
quicksort	B-Algorithm
.	O
</s>
<s>
Implementations	O
of	O
the	O
qsort	B-Language
function	O
achieve	O
polymorphism	B-Application
,	O
the	O
ability	O
to	O
sort	O
different	O
kinds	O
of	O
data	O
,	O
by	O
taking	O
a	O
function	B-Language
pointer	I-Language
to	O
a	O
three-way	O
comparison	O
function	O
,	O
as	O
well	O
as	O
a	O
parameter	O
that	O
specifies	O
the	O
size	O
of	O
its	O
individual	O
input	O
objects	O
.	O
</s>
<s>
A	O
qsort	B-Language
function	O
was	O
implemented	O
by	O
Lee	O
McMahon	O
in	O
1972	O
.	O
</s>
<s>
It	O
was	O
in	O
place	O
in	O
Version	B-Operating_System
3	I-Operating_System
Unix	I-Operating_System
as	O
a	O
library	O
function	O
,	O
but	O
was	O
then	O
an	O
assembler	B-Language
subroutine	O
.	O
</s>
<s>
A	O
C	O
version	O
,	O
with	O
roughly	O
the	O
interface	O
of	O
the	O
standard	O
C	O
version	O
,	O
was	O
in	O
place	O
in	O
Version	B-Operating_System
6	I-Operating_System
Unix	I-Operating_System
.	O
</s>
<s>
It	O
was	O
rewritten	O
in	O
1983	O
for	O
BSD	B-Operating_System
.	O
</s>
<s>
In	O
1991	O
,	O
Bell	O
Labs	O
employees	O
observed	O
that	O
McMahon	O
's	O
and	O
BSD	B-Operating_System
versions	O
of	O
qsort	B-Language
would	O
consume	O
quadratic	O
time	O
for	O
some	O
simple	O
inputs	O
.	O
</s>
<s>
The	O
following	O
piece	O
of	O
C	O
code	O
shows	O
how	O
to	O
sort	O
a	O
list	O
of	O
integers	O
using	O
qsort	B-Language
.	O
</s>
<s>
Since	O
the	O
comparison	O
function	O
of	O
the	O
original	O
qsort	B-Language
only	O
accepts	O
two	O
pointers	O
,	O
passing	O
in	O
additional	O
parameters	O
(	O
e.g.	O
</s>
<s>
The	O
issue	O
was	O
solved	O
by	O
the	O
BSD	B-Operating_System
and	O
GNU	B-Operating_System
Unix-like	B-Operating_System
systems	I-Operating_System
by	O
a	O
introducing	O
qsort_r	O
function	O
,	O
which	O
allows	O
for	O
an	O
additional	O
parameter	O
to	O
be	O
passed	O
to	O
the	O
comparison	O
function	O
.	O
</s>
<s>
C11	O
Annex	O
K	O
defines	O
a	O
qsort_s	O
essentially	O
identical	O
to	O
GNU	B-Operating_System
's	O
qsort_r	O
.	O
</s>
<s>
The	O
macOS	B-Application
and	O
FreeBSD	B-Operating_System
libcs	B-Language
also	O
contain	O
qsort_b	O
,	O
a	O
variant	O
that	O
uses	O
blocks	B-Language
,	O
an	O
analogue	O
to	O
closures	B-Language
,	O
as	O
an	O
alternate	O
solution	O
to	O
the	O
same	O
problem	O
.	O
</s>
