---
name: "qsort"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/qsort"
---

# qsort(3)

sort an array

## 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)](/feature_test_macros/7.md)):

**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)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **qsort**(), **qsort\_r**() | Thread safety | MT-Safe |

## STANDARDS

- **qsort**()

  C11, POSIX.1-2008.

## HISTORY

- **qsort**()

  POSIX.1-2001, C89, SVr4, 4.3BSD.

- **qsort\_r**()

  glibc 2.8.

## NOTES

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

## EXAMPLES

For one example of use, see the example under [**bsearch**(3)](/bsearch/3.md).

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);
}
```

## SEE ALSO

[**sort**(1)](/sort/1.md), [**alphasort**(3)](/alphasort/3.md), [**strcmp**(3)](/strcmp/3.md), [**versionsort**(3)](/versionsort/3.md)