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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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qsort(3) Library Functions Manual qsort(3)
qsort, qsort_r - sort an array
Standard C library (libc, -lc)
#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
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.
The qsort() and qsort_r() functions return no value.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ qsort(), qsort_r() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
qsort()
C11, POSIX.1-2008.
qsort()
POSIX.1-2001, C89, SVr4, 4.3BSD.
qsort_r()
glibc 2.8.
To compare C strings, the comparison function can call strcmp(3),
as shown in the example below.
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);
}
sort(1), alphasort(3), strcmp(3), versionsort(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-06-28 qsort(3)
Pages that refer to this page: bsearch(3), fts(3), scandir(3), tsearch(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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