man3/telldir.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified Sat Jul 24 17:48:42 1993 by Rik Faith (faith@cs.unc.edu)
  30 .TH TELLDIR 3  2017-09-15 "" "Linux Programmer's Manual"
  31 .SH NAME
  32 telldir \- return current location in directory stream
  33 .SH SYNOPSIS
  34 .nf
  35 .B #include <dirent.h>
  36 .PP
  37 .BI "long telldir(DIR *" dirp );
  38 .fi
  39 .PP
  40 .in -4n
  41 Feature Test Macro Requirements for glibc (see
  42 .BR feature_test_macros (7)):
  43 .in
  44 .PP
  45 .BR telldir ():
  46  _XOPEN_SOURCE
  47     || /* Glibc since 2.19: */ _DEFAULT_SOURCE
  48     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  49 .SH DESCRIPTION
  50 The
  51 .BR telldir ()
  52 function returns the current location associated with
  53 the directory stream \fIdirp\fP.
  54 .SH RETURN VALUE
  55 On success, the
  56 .BR telldir ()
  57 function returns the current location
  58 in the directory stream.
  59 On error, \-1 is returned, and
  60 .I errno
  61 is set appropriately.
  62 .SH ERRORS
  63 .TP
  64 .B EBADF
  65 Invalid directory stream descriptor \fIdirp\fP.
  66 .SH ATTRIBUTES
  67 For an explanation of the terms used in this section, see
  68 .BR attributes (7).
  69 .TS
  70 allbox;
  71 lb lb lb
  72 l l l.
  73 Interface       Attribute       Value
  74 T{
  75 .BR telldir ()
  76 T}      Thread safety   MT-Safe
  77 .TE
  78 .SH CONFORMING TO
  79 POSIX.1-2001, POSIX.1-2008, 4.3BSD.
  80 .SH NOTES
  81 In glibc up to version 2.1.1, the return type of
  82 .BR telldir ()
  83 was
  84 .IR off_t .
  85 POSIX.1-2001 specifies
  86 .IR long ,
  87 and this is the type used since glibc 2.1.2.
  88 .PP
  89 In early filesystems, the value returned by
  90 .BR telldir ()
  91 was a simple file offset within a directory.
  92 Modern filesystems use tree or hash structures, rather than flat tables,
  93 to represent directories.
  94 On such filesystems, the value returned by
  95 .BR telldir ()
  96 (and used internally by
  97 .BR readdir (3))
  98 is a "cookie" that is used by the implementation
  99 to derive a position within a directory.
 100 .\" https://lwn.net/Articles/544298/
 101 Application programs should treat this strictly as an opaque value, making
 102 .I no
 103 assumptions about its contents.
 104 .SH SEE ALSO
 105 .BR closedir (3),
 106 .BR opendir (3),
 107 .BR readdir (3),
 108 .BR rewinddir (3),
 109 .BR scandir (3),
 110 .BR seekdir (3)