Manpages - alphasort.3p

This manual page is part of the POSIX Programmer’s Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

alphasort, scandir — scan a directory

  #include <dirent.h>
  int alphasort(const struct dirent **d1, const struct dirent **d2);
  int scandir(const char *dir, struct dirent ***namelist,
      int (*sel)(const struct dirent *),
      int (*compar)(const struct dirent **, const struct dirent **));

The alphasort/() function can be used as the comparison function for the /scandir/() function to sort the directory entries, /d1 and d2, into alphabetical order. Sorting happens as if by calling the strcoll/() function on the /d_name element of the dirent structures passed as the two parameters. If the /strcoll/() function fails, the return value of /alphasort/() is unspecified.

The alphasort/() function shall not change the setting of /errno if successful. Since no return value is reserved to indicate an error, an application wishing to check for error situations should set errno to 0, then call alphasort/(), then check /errno.

The scandir/() function shall scan the directory /dir, calling the function referenced by sel on each directory entry. Entries for which the function referenced by sel returns non-zero shall be stored in strings allocated as if by a call to malloc/(), and sorted as if by a call to /qsort/() with the comparison function /compar, except that compar need not provide total ordering. The strings are collected in array namelist which shall be allocated as if by a call to malloc/(). If /sel is a null pointer, all entries shall be selected. If the comparison function compar does not provide total ordering, the order in which the directory entries are stored is unspecified.

Upon successful completion, the /alphasort/() function shall return an integer greater than, equal to, or less than 0, according to whether the name of the directory entry pointed to by d1 is lexically greater than, equal to, or less than the directory pointed to by d2 when both are interpreted as appropriate to the current locale. There is no return value reserved to indicate an error.

Upon successful completion, the /scandir/() function shall return the number of entries in the array and a pointer to the array through the parameter namelist. Otherwise, the /scandir/() function shall return -1.

The /scandir/() function shall fail if:

EACCES

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

ELOOP

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

ENAMETOOLONG

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

ENOENT

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

ENOMEM

Insufficient storage space is available.

ENOTDIR

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

EOVERFLOW

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

The /scandir/() function may fail if:

ELOOP

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

EMFILE

All file descriptors available to the process are currently open.

ENAMETOOLONG

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}.

ENFILE

Too many files are currently open in the system.

The following sections are informative.

An example to print the files in the current directory:

    #include <dirent.h>
    #include <stdio.h>
    #include <stdlib.h>
    ...
    struct dirent **namelist;
    int i,n;
        n = scandir(".", &namelist, 0, alphasort);
        if (n < 0)
            perror("scandir");
        else {
            for (i = 0; i < n; i++) {
                printf("%s\n", namelist[i]->d_name);
                free(namelist[i]);
                }
            }
        free(namelist);
    ...

If dir contains filenames that do not form character strings, or which contain characters outside the domain of the collating sequence of the current locale, the /alphasort/() function need not provide a total ordering. This condition is not possible if all filenames within the directory consist only of characters from the portable filename character set.

The /scandir/() function may allocate dynamic storage during its operation. If scandir/() is forcibly terminated, such as by /longjmp/() or /siglongjmp/() being executed by the function pointed to by /sel or compar, or by an interrupt routine, /scandir/() does not have a chance to free that storage, so it remains permanently allocated. A safe way to handle interrupts is to store the fact that an interrupt has occurred, then wait until /scandir/() returns to act on the interrupt.

For functions that allocate memory as if by /malloc/(), the application should release such memory when it is no longer required by a call to free/(). For /scandir/(), this is /namelist (including all of the individual strings in namelist).

None.

None.

/qsort ( )/, /strcoll ( )/

The Base Definitions volume of POSIX.1‐2017, <dirent.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology – Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

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