SCANDIR(3) | Library Functions Manual | SCANDIR(3)

# NAME

`scandir`, `scandirat`, `alphasort` — scan a directory

# SYNOPSIS

`#include <sys/types.h>`
`#include <dirent.h>`

int
`scandir`(const char *dirname, struct dirent ***namelist, int (*select)(const struct dirent *), int (*compar)(const struct dirent **, const struct dirent **));

int
`scandirat`(int dirfd, const char *dirname, struct dirent ***namelist, int (*select)(const struct dirent *), int (*compar)(const struct dirent **, const struct dirent **));

int
`alphasort`(const struct dirent **d1, const struct dirent **d2);

# DESCRIPTION

The `scandir`() function reads the directory dirname and builds an array of pointers to directory entries using malloc(3). It returns the number of entries in the array. A pointer to the array of directory entries is stored in the location referenced by namelist.

The select parameter is a pointer to a user-supplied subroutine which is called by `scandir`() to select which entries are to be included in the array. The select routine is passed a pointer to a directory entry and should return a non-zero value if the directory entry is to be included in the array. If select is `NULL`, then all directory entries will be included.

The compar parameter is a pointer to a user-supplied subroutine which is passed to qsort(3) to sort the completed array. If this pointer is `NULL`, the array is not sorted.

The `alphasort`() function is a routine which can be used for the compar parameter to sort the array alphabetically.

The memory allocated for the array can be deallocated with free(3), by freeing each pointer in the array and then the array itself.

The `scandirat`() function is similar to `scandir`(), but takes an additional dirfd argument. If dirname is relative, dirfd must be a valid file descriptor referencing a directory, in which case the dirname lookup is performed relative to the directory referenced by dirfd. If dirfd has the special value AT_FDCWD, then the current process directory is used as the base for relative lookups. See openat(2) for additional details.

# DIAGNOSTICS

Returns -1 if the directory cannot be opened for reading or if malloc(3) cannot allocate enough memory to hold all the data structures.

# SEE ALSO

malloc(3), opendir(3), qsort(3), dir(5)

# STANDARDS

The `scandir`() and `alphasort`() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).

# HISTORY

The `scandir`() and `alphasort`() functions appeared in 4.2BSD.

The argument types for `alphasort`() and for the compar argument to `scandir`() were originally void *, then changed to const void *, and then finally changed by IEEE Std 1003.1-2008 (“POSIX.1”) to their current form of const struct dirent **. Similarly, the `select`() argument to `scandir`() was originally struct dirent * until it was changed to its current form of const struct dirent *.

April 15, 2024 | Debian