scandir(3) Library Functions Manual scandir(3)
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,
int (*filter)(const struct dirent *),
int (*compar)(const struct dirent **,
const struct dirent **));
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,
int (*filter)(const struct dirent *),
int (*compar)(const struct dirent **,
const struct dirent **));
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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), sorted using qsort(3) with
the comparison function compar(), and collected in array namelist which
is allocated via malloc(3). If filter is NULL, all entries are se-
lected.
The alphasort() and versionsort() functions can be used as the compari-
son function compar(). The former sorts directory entries using str-
coll(3), the latter using strverscmp(3) 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 the pathname given in dirp is relative, then it is interpreted rela-
tive 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) for an explanation of the need for scandirat().
RETURN VALUE
The scandir() function returns the number of directory entries se-
lected. On error, -1 is returned, with errno set to indicate the er-
ror.
The alphasort() and versionsort() functions return an integer less
than, equal to, or greater than zero if the first argument is consid-
ered to be respectively less than, equal to, or greater than the sec-
ond.
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 a relative pathname and dirfd is a file
descriptor referring to a file other than a directory.
VERSIONS
versionsort() was added in glibc 2.1.
scandirat() was added in glibc 2.15.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌─────────────────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼────────────────┤
│scandir(), scandirat() │ Thread safety │ MT-Safe │
├─────────────────────────────────────┼───────────────┼────────────────┤
│alphasort(), versionsort() │ Thread safety │ MT-Safe locale │
└─────────────────────────────────────┴───────────────┴────────────────┘
STANDARDS
alphasort(), scandir(): 4.3BSD, POSIX.1-2008.
versionsort() and scandirat() are GNU extensions.
NOTES
Since glibc 2.1, alphasort() calls strcoll(3); earlier it used str-
cmp(3).
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), fnmatch(3), opendir(3), readdir(3), rewinddir(3),
seekdir(3), strcmp(3), strcoll(3), strverscmp(3), telldir(3)
Linux man-pages 6.03 2023-02-05 scandir(3)
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