1ALPHASORT(3P) POSIX Programmer's Manual ALPHASORT(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 alphasort, scandir — scan a directory
13
15 #include <dirent.h>
16 int alphasort(const struct dirent **d1, const struct dirent **d2);
18 int scandir(const char *dir, struct dirent ***namelist,
19 int (*sel)(const struct dirent *),
20 int (*compar)(const struct dirent **, const struct dirent **));
21
23 The alphasort() function can be used as the comparison function for the
24 scandir() function to sort the directory entries, d1 and d2, into
25 alphabetical order. Sorting happens as if by calling the strcoll()
26 function on the d_name element of the dirent structures passed as the
27 two parameters. If the strcoll() function fails, the return value of
28 alphasort() is unspecified.
29 The alphasort() function shall not change the setting of errno if suc‐
31 cessful. Since no return value is reserved to indicate an error, an
32 application wishing to check for error situations should set errno to
33 0, then call alphasort(), then check errno.
34 The scandir() function shall scan the directory dir, calling the func‐
36 tion referenced by sel on each directory entry. Entries for which the
37 function referenced by sel returns non-zero shall be stored in strings
38 allocated as if by a call to malloc(), and sorted as if by a call to
39 qsort() with the comparison function compar, except that compar need
40 not provide total ordering. The strings are collected in array namelist
41 which shall be allocated as if by a call to malloc(). If sel is a null
42 pointer, all entries shall be selected. If the comparison function
43 compar does not provide total ordering, the order in which the direc‐
44 tory entries are stored is unspecified.
45
47 Upon successful completion, the alphasort() function shall return an
48 integer greater than, equal to, or less than 0, according to whether
49 the name of the directory entry pointed to by d1 is lexically greater
50 than, equal to, or less than the directory pointed to by d2 when both
51 are interpreted as appropriate to the current locale. There is no
52 return value reserved to indicate an error.
53 Upon successful completion, the scandir() function shall return the
55 number of entries in the array and a pointer to the array through the
56 parameter namelist. Otherwise, the scandir() function shall return -1.
57
59 The scandir() function shall fail if:
60 EACCES Search permission is denied for the component of the path prefix
62 of dir or read permission is denied for dir.
63 ELOOP A loop exists in symbolic links encountered during resolution of
65 the dir argument.
66 ENAMETOOLONG
68 The length of a component of a pathname is longer than
69 {NAME_MAX}.
70 ENOENT A component of dir does not name an existing directory or dir is
72 an empty string.
73 ENOMEM Insufficient storage space is available.
75 ENOTDIR
77 A component of dir names an existing file that is neither a
78 directory nor a symbolic link to a directory.
79 EOVERFLOW
81 One of the values to be returned or passed to a callback func‐
82 tion cannot be represented correctly.
83 The scandir() function may fail if:
85 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
87 resolution of the dir argument.
88 EMFILE All file descriptors available to the process are currently
90 open.
91 ENAMETOOLONG
93 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
94 tion of a symbolic link produced an intermediate result with a
95 length that exceeds {PATH_MAX}.
96 ENFILE Too many files are currently open in the system.
98 The following sections are informative.
100
102 An example to print the files in the current directory:
103 #include <dirent.h>
106 #include <stdio.h>
107 #include <stdlib.h>
108 ...
109 struct dirent **namelist;
110 int i,n;
111 n = scandir(".", &namelist, 0, alphasort);
113 if (n < 0)
114 perror("scandir");
115 else {
116 for (i = 0; i < n; i++) {
117 printf("%s\n", namelist[i]->d_name);
118 free(namelist[i]);
119 }
120 }
121 free(namelist);
122 ...
123
125 If dir contains filenames that do not form character strings, or which
126 contain characters outside the domain of the collating sequence of the
127 current locale, the alphasort() function need not provide a total
128 ordering. This condition is not possible if all filenames within the
129 directory consist only of characters from the portable filename charac‐
130 ter set.
131 The scandir() function may allocate dynamic storage during its opera‐
133 tion. If scandir() is forcibly terminated, such as by longjmp() or sig‐
134 longjmp() being executed by the function pointed to by sel or compar,
135 or by an interrupt routine, scandir() does not have a chance to free
136 that storage, so it remains permanently allocated. A safe way to handle
137 interrupts is to store the fact that an interrupt has occurred, then
138 wait until scandir() returns to act on the interrupt.
139 For functions that allocate memory as if by malloc(), the application
141 should release such memory when it is no longer required by a call to
142 free(). For scandir(), this is namelist (including all of the individ‐
143 ual strings in namelist).
144
146 None.
147
149 None.
150
152 qsort(), strcoll()
153 The Base Definitions volume of POSIX.1‐2017, <dirent.h>
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157 Portions of this text are reprinted and reproduced in electronic form
158 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
159 table Operating System Interface (POSIX), The Open Group Base Specifi‐
160 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
161 Electrical and Electronics Engineers, Inc and The Open Group. In the
162 event of any discrepancy between this version and the original IEEE and
163 The Open Group Standard, the original IEEE and The Open Group Standard
164 is the referee document. The original Standard can be obtained online
165 at http://www.opengroup.org/unix/online.html .
166 Any typographical or formatting errors that appear in this page are
168 most likely to have been introduced during the conversion of the source
169 files to man page format. To report such errors, see https://www.ker‐
170 nel.org/doc/man-pages/reporting_bugs.html .
171IEEE/The Open Group 2017 ALPHASORT(3P)