man-pages/man3/scandir.3

.\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 18:26:16 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Thu Apr 11 17:11:33 1996 by Andries Brouwer (aeb@cwi.nl):
.\"     Corrected type of compar routines, as suggested by
.\"     Miguel Barreiro (enano@avalon.yaix.es).  Added example.
.\" Modified Sun Sep 24 20:15:46 2000 by aeb, following Petter Reinholdtsen.
.\" Modified 2001-12-26 by aeb, following Joey. Added versionsort.
.\"
.\" FIXME glibc 2.15 adds scandirat()
.\"
.TH SCANDIR 3  2009-02-10 "GNU" "Linux Programmer's Manual"
.SH NAME
scandir, alphasort, versionsort \- scan a directory for matching entries
.SH SYNOPSIS
.nf
.B #include <dirent.h>
.sp
.BI "int scandir(const char *" dirp ", struct dirent ***" namelist ,
.RS
.BI "int (*" filter ")(const struct dirent *),"
.BI "int (*" compar ")(const struct dirent **, const struct dirent **));"
.RE
.sp
.BI "int alphasort(const void *" a ", const void *" b );
.sp
.BI "int versionsort(const void *" a ", const void *" b );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR scandir (),
.BR alphasort ():
_BSD_SOURCE || _SVID_SOURCE
.br
.BR versionsort ():
_GNU_SOURCE
.SH DESCRIPTION
The
.BR scandir ()
function scans the directory \fIdirp\fP, calling
\fIfilter\fP() on each directory entry.
Entries for which
\fIfilter\fP() returns nonzero are stored in strings allocated via
.BR malloc (3),
sorted using
.BR qsort (3)
with the comparison
function \fIcompar\fP(), and collected in array \fInamelist\fP
which is allocated via
.BR malloc (3).
If \fIfilter\fP is NULL, all entries are selected.
.LP
The
.BR alphasort ()
and
.BR versionsort ()
functions can be used as the comparison function
.IR compar ().
The former sorts directory entries using
.BR strcoll (3),
the latter using
.BR strverscmp (3)
on the strings \fI(*a)\->d_name\fP and \fI(*b)\->d_name\fP.
.SH "RETURN VALUE"
The
.BR scandir ()
function returns the number of directory entries
selected or \-1 if an error occurs.
.PP
The
.BR alphasort ()
and
.BR 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.
.SH ERRORS
.TP
.B ENOMEM
Insufficient memory to complete the operation.
.SH VERSIONS
.BR versionsort ()
was added to glibc in version 2.1.
.SH "CONFORMING TO"
.BR alphasort ()
and
.BR scandir ()
are specified in POSIX.1-2008, and are widely available.
.BR versionsort ()
is a GNU extension.
.LP
The functions
.BR scandir ()
and
.BR alphasort ()
are from 4.3BSD, and have been available under Linux since libc4.
Libc4 and libc5 use the more precise prototype
.sp
.nf
    int alphasort(const struct dirent ** a,
                  const struct dirent **b);
.fi
.sp
but glibc 2.0 returns to the imprecise BSD prototype.
.LP
The function
.BR versionsort ()
is a GNU extension, available since glibc 2.1.
.LP
Since glibc 2.1,
.BR alphasort ()
calls
.BR strcoll (3);
earlier it used
.BR strcmp (3).
.SH EXAMPLE
.nf
#define _SVID_SOURCE
/* print files in current directory in reverse order */
#include <dirent.h>

int
main(void)
{
    struct dirent **namelist;
    int n;

    n = scandir(".", &namelist, 0, alphasort);
    if (n < 0)
        perror("scandir");
    else {
        while (n\-\-) {
            printf("%s\en", namelist[n]\->d_name);
            free(namelist[n]);
        }
        free(namelist);
    }
}
.fi
.SH "SEE ALSO"
.BR closedir (3),
.BR fnmatch (3),
.BR opendir (3),
.BR readdir (3),
.BR rewinddir (3),
.BR seekdir (3),
.BR strcmp (3),
.BR strcoll (3),
.BR strverscmp (3),
.BR telldir (3)