scandir(3C)

NAME

scandir(), alphasort() — scan a directory

SYNOPSIS

#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 alphasort( 
     const struct dirent **d1, 
     const struct dirent **d2 
); 

DESCRIPTION

scandir() reads the directory dirname and builds an array of pointers to directory entries using malloc() (see malloc(3C)). It returns the number of entries in the array and a pointer to the array through 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 the directory entries will be included.

The compar parameter is a pointer to a user-supplied subroutine which is passed to qsort(3C) to sort the completed array. If this pointer is null, the array is not sorted. alphasort() 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() (see malloc(3C)) by freeing each pointer in the array and the array itself.

APPLICATION USAGE

scandir() is thread-safe. It is not async-cancel-safe. A cancellation point may occur when a thread is executing scandir().

EXTERNAL INFLUENCES

Locale

The LC_COLLATE category determines the collation ordering used by alphasort(). See hpnls(5) for a description of supported collation features.

The LC_CTYPE category determines the interpretation of bytes in the file name portion of directory entries as single- and/or multi-byte characters by the alphasort() function.

Results are undefined if the locales specified by the LC_COLLATE and LC_CTYPE categories use different code sets.

International Code Set Support

Single- and multi-byte character code sets are supported for alphasort().

RETURN VALUE

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

EXAMPLE

The example program below scans the /tmp directory. It does not exclude any entries since select is NULL. The contents of namelist are sorted by alphasort(). It prints out how many entries are in /tmp and the sorted entries of the /tmp directory. The memory used by scandir() is returned using free().

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

extern int scandir();
extern int alphasort();

main()
{
    int num_entries, i;
    struct dirent **namelist, **list;

    if ((num_entries =
             scandir("/tmp", &namelist, NULL, alphasort)) < 0) {
        fprintf(stderr, "Unexpected error\n");
        exit(1);
    }
    printf("Number of entries is %d\n", num_entries);
    if (num_entries) {
        printf("Entries are:");
        for (i=0, list=namelist; i<num_entries; i++) {
            printf(" %s", (*list)->d_name);
            free(*list);
            list++;
        }
        free(namelist);
        printf("\n");
    }
    printf("\n");
    exit(0);
}