Linux man page for scandir.3

scandir(3) -- Linux man page

NAME

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

SYNOPSIS

#include <dirent.h>

int scandir(const char *dir, struct dirent ***namelist,
int(*filter)(const struct dirent *),
int(*compar)(const struct dirent **, const struct dirent **));


int alphasort(const void *a, const void *b);


int versionsort(const void *a, const void *b);

DESCRIPTION

The scandir() function scans the directory dir, calling filter() on each directory entry. Entries for which filter() returns non-zero are stored in strings allocated via malloc(), sorted using qsort() with the comparison function compar(), and collected in array namelist which is allocated via malloc(). 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), the latter using strverscmp(3) on the strings (*a)->d_name and (*b)->d_name.

RETURN VALUE

The scandir() function returns the number of directory entries selected or -1 if an error occurs.

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

ENOMEM: Insufficient memory to complete the operation.

CONFORMING TO

None of these functions is in POSIX. LSB has deprecated the library call alphasort() and never contained scandir().

The functions scandir() and alphasort() are from BSD 4.3, and have been available under Linux since libc4. Libc4 and libc5 use the more precise prototype

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

but glibc 2.0 returns to the imprecise BSD prototype.

The function versionsort() is a GNU extension, available since glibc 2.1. Since glibc 2.1, alphasort() calls strcoll(3); earlier it used strcmp(3).

EXAMPLE

/* print files in current directory in reverse order */
#include <dirent.h>
main(){
    struct dirent **namelist;
    int n;

    n = scandir(".", &namelist, 0, alphasort);
    if (n < 0)
        perror("scandir");
    else {
        while(n--) {
            printf("%s\n", namelist[n]->d_name);
            free(namelist[n]);
        }
        free(namelist);
    }
}