man3/readdir_r.3

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  26 .TH READDIR_R 3  2016-03-01 "" "Linux Programmer's Manual"
  27 .SH NAME
  28 readdir_r \- read a directory
  29 .SH SYNOPSIS
  30 .nf
  31 .B #include <dirent.h>
  32 .PP
  33 .BI "int readdir_r(DIR *" dirp ", struct dirent *" entry \
  34 ", struct dirent **" result );
  35 .fi
  36 .PP
  37 .in -4n
  38 Feature Test Macro Requirements for glibc (see
  39 .BR feature_test_macros (7)):
  40 .ad l
  41 .in
  42 .PP
  43 .BR readdir_r ():
  44 .RS 4
  45 _POSIX_C_SOURCE
  46     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  47 .RE
  48 .ad b
  49 .SH DESCRIPTION
  50 This function is deprecated; use
  51 .BR readdir (3)
  52 instead.
  53 .PP
  54 The
  55 .BR readdir_r ()
  56 function was invented as a reentrant version of
  57 .BR readdir (3).
  58 It reads the next directory entry from the directory stream
  59 .IR dirp ,
  60 and returns it in the caller-allocated buffer pointed to by
  61 .IR entry .
  62 For details of the
  63 .IR dirent
  64 structure, see
  65 .BR readdir (3).
  66 .PP
  67 A pointer to the returned buffer is placed in
  68 .IR *result ;
  69 if the end of the directory stream was encountered,
  70 then NULL is instead returned in
  71 .IR *result .
  72 .PP
  73 It is recommended that applications use
  74 .BR readdir (3)
  75 instead of
  76 .BR readdir_r ().
  77 Furthermore, since version 2.24, glibc deprecates
  78 .BR readdir_r ().
  79 The reasons are as follows:
  80 .IP * 3
  81 On systems where
  82 .BR NAME_MAX
  83 is undefined, calling
  84 .BR readdir_r ()
  85 may be unsafe because the interface does not allow the caller to specify
  86 the length of the buffer used for the returned directory entry.
  87 .IP *
  88 On some systems,
  89 .BR readdir_r ()
  90 can't read directory entries with very long names.
  91 When the glibc implementation encounters such a name,
  92 .BR readdir_r ()
  93 fails with the error
  94 .B ENAMETOOLONG
  95 .IR "after the final directory entry has been read" .
  96 On some other systems,
  97 .BR readdir_r ()
  98 may return a success status, but the returned
  99 .IR d_name
 100 field may not be null terminated or may be truncated.
 101 .IP *
 102 In the current POSIX.1 specification (POSIX.1-2008),
 103 .BR readdir (3)
 104 is not required to be thread-safe.
 105 However, in modern implementations (including the glibc implementation),
 106 concurrent calls to
 107 .BR readdir (3)
 108 that specify different directory streams are thread-safe.
 109 Therefore, the use of
 110 .BR readdir_r ()
 111 is generally unnecessary in multithreaded programs.
 112 In cases where multiple threads must read from the same directory stream,
 113 using
 114 .BR readdir (3)
 115 with external synchronization is still preferable to the use of
 116 .BR readdir_r (),
 117 for the reasons given in the points above.
 118 .IP *
 119 It is expected that a future version of POSIX.1
 120 .\" FIXME .
 121 .\" http://www.austingroupbugs.net/view.php?id=696
 122 will make
 123 .BR readdir_r ()
 124 obsolete, and require that
 125 .BR readdir (3)
 126 be thread-safe when concurrently employed on different directory streams.
 127 .SH RETURN VALUE
 128 The
 129 .BR readdir_r ()
 130 function returns 0 on success.
 131 On error, it returns a positive error number (listed under ERRORS).
 132 If the end of the directory stream is reached,
 133 .BR readdir_r ()
 134 returns 0, and returns NULL in
 135 .IR *result .
 136 .SH ERRORS
 137 .TP
 138 .B EBADF
 139 Invalid directory stream descriptor \fIdirp\fP.
 140 .TP
 141 .B ENAMETOOLONG
 142 A directory entry whose name was too long to be read was encountered.
 143 .SH ATTRIBUTES
 144 For an explanation of the terms used in this section, see
 145 .BR attributes (7).
 146 .TS
 147 allbox;
 148 lb lb lb
 149 l l l.
 150 Interface       Attribute       Value
 151 T{
 152 .BR readdir_r ()
 153 T}      Thread safety   MT-Safe
 154 .TE
 155 .SH CONFORMING TO
 156 POSIX.1-2001, POSIX.1-2008.
 157 .SH SEE ALSO
 158 .BR readdir (3)