.\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk) .\" and Copyright (C) 2008, 2016 Michael Kerrisk .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" References consulted: .\" Linux libc source code .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) .\" 386BSD man pages .\" Modified Sat Jul 24 16:09:49 1993 by Rik Faith (faith@cs.unc.edu) .\" Modified 11 June 1995 by Andries Brouwer (aeb@cwi.nl) .\" Modified 22 July 1996 by Andries Brouwer (aeb@cwi.nl) .\" 2007-07-30 Ulrich Drepper , mtk: .\" Rework discussion of nonstandard structure fields. .\" .TH READDIR 3 2016-03-15 "" "Linux Programmer's Manual" .SH NAME readdir \- read a directory .SH SYNOPSIS .nf .B #include .sp .BI "struct dirent *readdir(DIR *" dirp ); .fi .SH DESCRIPTION The .BR readdir () function returns a pointer to a \fIdirent\fP structure representing the next directory entry in the directory stream pointed to by \fIdirp\fP. It returns NULL on reaching the end of the directory stream or if an error occurred. .PP In the glibc implementation, the .I dirent structure is defined as follows: .PP .in +4n .nf struct dirent { ino_t d_ino; /* Inode number */ off_t d_off; /* Not an offset; see below */ unsigned short d_reclen; /* Length of this record */ unsigned char d_type; /* Type of file; not supported by all filesystem types */ char d_name[256]; /* Null-terminated filename */ }; .fi .in .PP The only fields in the .I dirent structure that are mandated by POSIX.1 are .IR d_name and .IR d_ino . The other fields are unstandardized, and not present on all systems; see NOTES below for some further details. The fields of the .I dirent structure are as follows: .TP .I d_ino This is the inode number of the file. .TP .I d_off The value returned in .I d_off is the same as would be returned by calling .BR telldir (3) at the current position in the directory stream. Be aware that despite its type and name, the .I d_off field is seldom any kind of directory offset on modern filesystems. .\" https://lwn.net/Articles/544298/ Applications should treat this field as an opaque value, making no assumptions about its contents; see also .BR telldir (3). .TP .I d_reclen This is the size (in bytes) of the returned record. This may not match the size of the structure definition shown above; see NOTES. .TP .I d_type This field contains a value indicating the file type, making it possible to avoid the expense of calling .BR lstat (2) if further actions depend on the type of the file. .IP When a suitable feature test macro is defined .RB ( _DEFAULT_SOURCE on glibc versions since 2.19, or .BR _BSD_SOURCE on glibc versions 2.19 and earlier), glibc defines the following macro constants for the value returned in .IR d_type : .RS .TP 12 .B DT_BLK This is a block device. .TP .B DT_CHR This is a character device. .TP .B DT_DIR This is a directory. .TP .B DT_FIFO This is a named pipe (FIFO). .TP .B DT_LNK This is a symbolic link. .TP .B DT_REG This is a regular file. .TP .B DT_SOCK This is a UNIX domain socket. .TP .B DT_UNKNOWN The file type could not be determined. .RE .IP Currently, .\" kernel 2.6.27 .\" The same sentence is in getdents.2 only some filesystems (among them: Btrfs, ext2, ext3, and ext4) have full support for returning the file type in .IR d_type . All applications must properly handle a return of .BR DT_UNKNOWN . .TP .I d_name This field contains the null terminated filename. .IR "See NOTES" . .PP The data returned by .BR readdir () may be overwritten by subsequent calls to .BR readdir () for the same directory stream. .SH RETURN VALUE On success, .BR readdir () returns a pointer to a .I dirent structure. (This structure may be statically allocated; do not attempt to .BR free (3) it.) If the end of the directory stream is reached, NULL is returned and .I errno is not changed. If an error occurs, NULL is returned and .I errno is set appropriately. To distinguish end of stream and from an error, set .I errno to zero before calling .BR readdir () and then check the value of .I errno if NULL is returned. .SH ERRORS .TP .B EBADF Invalid directory stream descriptor \fIdirp\fP. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lb lb lb l l l. Interface Attribute Value T{ .BR readdir () T} Thread safety MT-Unsafe race:dirstream .TE .PP In the current POSIX.1 specification (POSIX.1-2008), .BR readdir () is not required to be thread-safe. However, in modern implementations (including the glibc implementation), concurrent calls to .BR readdir () that specify different directory streams are thread-safe. In cases where multiple threads must read from the same directory stream, using .BR readdir () with external synchronization is still preferable to the use of the deprecated .BR readdir_r (3) function. It is expected that a future version of POSIX.1 .\" FIXME . .\" http://www.austingroupbugs.net/view.php?id=696 will require that .BR readdir () be thread-safe when concurrently employed on different directory streams. .SH CONFORMING TO POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. .SH NOTES A directory stream is opened using .BR opendir (3). The order in which filenames are read by successive calls to .BR readdir () depends on the filesystem implementation; it is unlikely that the names will be sorted in any fashion. Only the fields .I d_name and (as an XSI extension) .I d_ino are specified in POSIX.1. .\" POSIX.1-2001, POSIX.1-2008 Other than Linux, the .I d_type field is available mainly only on BSD systems. The remaining fields are available on many, but not all systems. Under glibc, programs can check for the availability of the fields not defined in POSIX.1 by testing whether the macros .BR _DIRENT_HAVE_D_NAMLEN , .BR _DIRENT_HAVE_D_RECLEN , .BR _DIRENT_HAVE_D_OFF , or .B _DIRENT_HAVE_D_TYPE are defined. .\" .SS The d_name field The .I dirent structure definition shown above is taken from the glibc headers, and shows the .I d_name field with a fixed size. .IR Warning : applications should avoid any dependence on the size of the .I d_name field. POSIX defines it as .IR "char\ d_name[]", a character array of unspecified size, with at most .B NAME_MAX characters preceding the terminating null byte (\(aq\\0\(aq). POSIX.1 explicitly notes that this field should not be used as an lvalue. The standard also notes that the use of .I sizeof(d_name) is incorrect; use .IR strlen(d_name) instead. (On some systems, this field is defined as .IR char\ d_name[1] !) By implication, the use .IR "sizeof(struct dirent)" to capture the size of the record including the size of .IR d_name is also incorrect. Note that while the call fpathconf(fd, _PC_NAME_MAX) returns the value 255 for most filesystems, on some filesystems (e.g., CIFS, Windows SMB servers), the null-terminated filename that is (correctly) returned in .I d_name can actually exceed this size. In such cases, the .I d_reclen field will contain a value that exceeds the size of the glibc .I dirent structure shown above. .SH SEE ALSO .BR getdents (2), .BR read (2), .BR closedir (3), .BR dirfd (3), .BR ftw (3), .BR offsetof (3), .BR opendir (3), .BR readdir_r (3), .BR rewinddir (3), .BR scandir (3), .BR seekdir (3), .BR telldir (3) .SH COLOPHON This page is part of release 4.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.