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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022



scandir, alphasort - scan a directory


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

int scandir(const char *dirname, struct dirent *(*namelist[]),
     int (*select)(const struct dirent *),
     int (*dcomp)(const struct dirent  **,
     const struct dirent **));
int alphasort(const struct dirent **d1,
     const struct dirent **d2);


The scandir() function reads the directory dirname using readdir(3C) and builds an array of pointers to directory entries using malloc(3C). The namelist argument is a pointer to an array of structure pointers. The select argument is a pointer to a routine that is called with a pointer to a directory entry and returns a non-zero value if the directory entry is included in the array. If this pointer is NULL, then all the directory entries are included. The dcomp argument is a pointer to a routine that is passed to qsort(3C), which sorts the completed array. If this pointer is NULL, the array is not sorted.

The alphasort() function can be used as the dcomp() function parameter for the scandir() function to sort the directory entries into alphabetical order, as if by the strcoll(3C) function. Its arguments are the two directory entries to compare.

Return Values

The scandir() function returns the number of entries in the array and a pointer to the array through the namelist argument. When an error is encountered, scandir() returns -1 and errno is set to indicate the error.

The alphasort() function returns an integer greater than, equal to, or less than 0 if the directory entry name pointed to by d1 is greater than, equal to, or less than the directory entry name pointed to by d2 when both are interpreted as appropriate to the current locale. There is no return value reserved to indicate an error.


The scandir() function will fail if:


Search permission is denied for the component of the path prefix of dir or read permission is denied for dir.


A loop exists in the symbolic links encountered during resolving the dir argument.


The length of a component of a pathname is longer than {NAME_MAX}.


A component of dir does not name an existing directory or dir is an empty string.


Insufficient storage space.


A component of dir names an existing file that is neither a directory nor a symbolic link to a directory.


One of the values to be returned or passed to a callback function cannot be represented correctly.

The scandir() function may fail if:


More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the dir argument.


All file descriptors available to the process are currently open.


The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length that exceeds {PATH_MAX}.


Too many files are currently open in the system.


The scandir() and alphasort() functions have transitional interfaces for 64-bit file offsets. See lf64(7).


See attributes(7) for descriptions of the following attributes:

Interface Stability
See below.

The scandir() function is Unsafe. The alphasort() function is Safe.

See Also

malloc(3C), qsort(3C), readdir(3C), strcoll(3C), attributes(7), lf64(7)