man-pages/man3p/opendir.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "OPENDIR" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" opendir 
.SH NAME
opendir \- open a directory
.SH SYNOPSIS
.LP
\fB#include <dirent.h>
.br
.sp
DIR *opendir(const char *\fP\fIdirname\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fIopendir\fP() function shall open a directory stream corresponding
to the directory named by the \fIdirname\fP argument.
The directory stream is positioned at the first entry. If the type
\fBDIR\fP is implemented using a file descriptor, applications
shall only be able to open up to a total of {OPEN_MAX} files and directories.
.SH RETURN VALUE
.LP
Upon successful completion, \fIopendir\fP() shall return a pointer
to an object of type \fBDIR\fP. Otherwise, a null pointer
shall be returned and \fIerrno\fP set to indicate the error.
.SH ERRORS
.LP
The \fIopendir\fP() function shall fail if:
.TP 7
.B EACCES
Search permission is denied for the component of the path prefix of
\fIdirname\fP or read permission is denied for
\fIdirname\fP.
.TP 7
.B ELOOP
A loop exists in symbolic links encountered during resolution of the
\fIdirname\fP argument.
.TP 7
.B ENAMETOOLONG
The length of the \fIdirname\fP argument exceeds {PATH_MAX} or a pathname
component is longer than {NAME_MAX}.
.TP 7
.B ENOENT
A component of \fIdirname\fP does not name an existing directory or
\fIdirname\fP is an empty string.
.TP 7
.B ENOTDIR
A component of \fIdirname\fP is not a directory.
.sp
.LP
The \fIopendir\fP() function may fail if:
.TP 7
.B ELOOP
More than {SYMLOOP_MAX} symbolic links were encountered during resolution
of the \fIdirname\fP argument.
.TP 7
.B EMFILE
{OPEN_MAX} file descriptors are currently open in the calling process.
.TP 7
.B ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the \fIdirname\fP
argument, the length of the substituted pathname
string exceeded {PATH_MAX}.
.TP 7
.B ENFILE
Too many files are currently open in the system.
.sp
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Open a Directory Stream
.LP
The following program fragment demonstrates how the \fIopendir\fP()
function is used.
.sp
.RS
.nf

\fB#include <sys/types.h>
#include <dirent.h>
#include <libgen.h>
\&...
    DIR *dir;
    struct dirent *dp;
\&...
    if ((dir = opendir (".")) == NULL) {
        perror ("Cannot open .");
        exit (1);
    }
.sp

    while ((dp = readdir (dir)) != NULL) {
\&...
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
The \fIopendir\fP() function should be used in conjunction with \fIreaddir\fP(),
\fIclosedir\fP(), and \fIrewinddir\fP() to
examine the contents of the directory (see the EXAMPLES section in
\fIreaddir\fP() ). This method is
recommended for portability.
.SH RATIONALE
.LP
Based on historical implementations, the rules about file descriptors
apply to directory streams as well. However, this volume
of IEEE\ Std\ 1003.1-2001 does not mandate that the directory stream
be implemented using file descriptors. The description
of \fIclosedir\fP() clarifies that if a file descriptor is used for
the directory stream,
it is mandatory that \fIclosedir\fP() deallocate the file descriptor.
When a file
descriptor is used to implement the directory stream, it behaves as
if the FD_CLOEXEC had been set for the file descriptor.
.LP
The directory entries for dot and dot-dot are optional. This volume
of IEEE\ Std\ 1003.1-2001 does not provide a way to
test \fIa priori\fP for their existence because an application that
is portable must be written to look for (and usually ignore)
those entries. Writing code that presumes that they are the first
two entries does not always work, as many implementations permit
them to be other than the first two entries, with a "normal" entry
preceding them. There is negligible value in providing a way
to determine what the implementation does because the code to deal
with dot and dot-dot must be written in any case and because
such a flag would add to the list of those flags (which has proven
in itself to be objectionable) and might be abused.
.LP
Since the structure and buffer allocation, if any, for directory operations
are defined by the implementation, this volume of
IEEE\ Std\ 1003.1-2001 imposes no portability requirements for erroneous
program constructs, erroneous data, or the use of
unspecified values such as the use or referencing of a \fIdirp\fP
value or a \fBdirent\fP structure value after a directory
stream has been closed or after a \fIfork\fP() or one of the \fIexec\fP
function calls.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIclosedir\fP() , \fIlstat\fP() , \fIreaddir\fP() , \fIrewinddir\fP()
, \fIsymlink\fP()
, the Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<dirent.h>\fP,
\fI<limits.h>\fP, \fI<sys/types.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .