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

# alphasort(3)

scan a directory for matching entries

Part of [scandir(3)](/scandir/3.md).

## NAME

scandir, scandirat, alphasort, versionsort - scan a directory for matching entries

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <dirent.h>
```

**int scandir(const char \*restrict** *dirp***,**             **struct dirent \*\*\*restrict** *namelist***,**             **typeof(int (const struct dirent \*)) \****filter***,**             **typeof(int (const struct dirent \*\*, const struct dirent \*\*))**                 **\****compar***);**

**int alphasort(const struct dirent \*\****a***, const struct dirent \*\****b***);** **int versionsort(const struct dirent \*\****a***, const struct dirent \*\****b***);**

**#include \<fcntl.h\>**          /\* Definition of AT\_\* constants \*/ **#include \<dirent.h\>**

**int scandirat(int** *dirfd***, const char \*restrict** *dirp***,**             **struct dirent \*\*\*restrict** *namelist***,**             **typeof(int (const struct dirent \*)) \****filter***,**             **typeof(int (const struct dirent \*\*, const struct dirent \*\*))**                 **\****compar***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**scandir**(), **alphasort**():

```
    /* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200809L
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

**versionsort**():

```
    _GNU_SOURCE
```

**scandirat**():

```
    _GNU_SOURCE
```

## DESCRIPTION

The **scandir**() function scans the directory *dirp*, calling *filter*() on each directory entry. Entries for which *filter*() returns nonzero are stored in strings allocated via [**malloc**(3)](/malloc/3.md), sorted using [**qsort**(3)](/qsort/3.md) with the comparison function *compar*(), and collected in array *namelist* which is allocated via [**malloc**(3)](/malloc/3.md). If *filter* is NULL, all entries are selected.

The **alphasort**() and **versionsort**() functions can be used as the comparison function *compar*(). The former sorts directory entries using [**strcoll**(3)](/strcoll/3.md), the latter using [**strverscmp**(3)](/strverscmp/3.md) on the strings *(\*a)-\>d\_name* and *(\*b)-\>d\_name*.

### scandirat()

The **scandirat**() function operates in exactly the same way as **scandir**(), except for the differences described here.

If *dirp* is relative, then it is interpreted relative to the directory referred to by the file descriptor *dirfd* (rather than relative to the current working directory of the calling process, as is done by **scandir**() for a relative pathname).

If *dirp* is relative and *dirfd* is the special value **AT\_FDCWD**, then *dirp* is interpreted relative to the current working directory of the calling process (like **scandir**()).

If *dirp* is absolute, then *dirfd* is ignored.

See [**openat**(2)](/openat/2.md) for an explanation of the need for **scandirat**().

## RETURN VALUE

The **scandir**() function returns the number of directory entries selected. On error, -1 is returned, with *errno* set to indicate the error.

The **alphasort**() and **versionsort**() functions 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.

## ERRORS

- **EBADF**

  (**scandirat**()) *dirp* is relative but *dirfd* is neither **AT\_FDCWD** nor a valid file descriptor.

- **ENOENT**

  The path in *dirp* does not exist.

- **ENOMEM**

  Insufficient memory to complete the operation.

- **ENOTDIR**

  The path in *dirp* is not a directory.

- **ENOTDIR**

  (**scandirat**()) *dirp* is relative and *dirfd* is a file descriptor referring to a file other than a directory.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **scandir**(), **scandirat**() | Thread safety | MT-Safe |
| **alphasort**(), **versionsort**() | Thread safety | MT-Safe locale |

## STANDARDS

- **alphasort**() **scandir**()

  POSIX.1-2008.

- **versionsort**() **scandirat**()

  GNU.

## HISTORY

- **alphasort**() **scandir**()

  4\.3BSD, POSIX.1-2008.

- **versionsort**()

  glibc 2.1.

- **scandirat**()

  glibc 2.15.

## NOTES

Since glibc 2.1, **alphasort**() calls [**strcoll**(3)](/strcoll/3.md); earlier it used [**strcmp**(3)](/strcmp/3.md).

Before glibc 2.10, the two arguments of **alphasort**() and **versionsort**() were typed as *const void \**. When **alphasort**() was standardized in POSIX.1-2008, the argument type was specified as the type-safe *const struct dirent \*\**, and glibc 2.10 changed the definition of **alphasort**() (and the nonstandard **versionsort**()) to match the standard.

## EXAMPLES

The program below prints a list of the files in the current directory in reverse order.

### Program source

```
#define _DEFAULT_SOURCE
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
    struct dirent **namelist;
    int n;
    n = scandir(".", &namelist, NULL, alphasort);
    if (n == -1) {
        perror("scandir");
        exit(EXIT_FAILURE);
    }
    while (n--) {
        printf("%s\n", namelist[n]->d_name);
        free(namelist[n]);
    }
    free(namelist);
    exit(EXIT_SUCCESS);
}
```

## SEE ALSO

[**closedir**(3)](/closedir/3.md), [**fnmatch**(3)](/fnmatch/3.md), [**opendir**(3)](/opendir/3.md), [**readdir**(3)](/readdir/3.md), [**rewinddir**(3)](/rewinddir/3.md), [**seekdir**(3)](/seekdir/3.md), [**strcmp**(3)](/strcmp/3.md), [**strcoll**(3)](/strcoll/3.md), [**strverscmp**(3)](/strverscmp/3.md), [**telldir**(3)](/telldir/3.md)