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OPENDIR

OPENDIR

Section: POSIX Programmer's Manual (P) Updated: 2003
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NAME

opendir - open a directory  

SYNOPSIS

#include <dirent.h>

DIR *opendir(const char *dirname);
 

DESCRIPTION

The opendir() function shall open a directory stream corresponding to the directory named by the dirname argument. The directory stream is positioned at the first entry. If the type DIR is implemented using a file descriptor, applications shall only be able to open up to a total of {OPEN_MAX} files and directories.  

RETURN VALUE

Upon successful completion, opendir() shall return a pointer to an object of type DIR. Otherwise, a null pointer shall be returned and errno set to indicate the error.  

ERRORS

The opendir() function shall fail if:

EACCES
Search permission is denied for the component of the path prefix of dirname or read permission is denied for dirname.
ELOOP
A loop exists in symbolic links encountered during resolution of the dirname argument.
ENAMETOOLONG
The length of the dirname argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
ENOENT
A component of dirname does not name an existing directory or dirname is an empty string.
ENOTDIR
A component of dirname is not a directory.

The opendir() function may fail if:

ELOOP
More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the dirname argument.
EMFILE
{OPEN_MAX} file descriptors are currently open in the calling process.
ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the dirname argument, the length of the substituted pathname string exceeded {PATH_MAX}.
ENFILE
Too many files are currently open in the system.

The following sections are informative.  

EXAMPLES

 

Open a Directory Stream

The following program fragment demonstrates how the opendir() function is used.


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


    while ((dp = readdir (dir)) != NULL) {
...

 

APPLICATION USAGE

The opendir() function should be used in conjunction with readdir(), closedir(), and rewinddir() to examine the contents of the directory (see the EXAMPLES section in readdir() ). This method is recommended for portability.  

RATIONALE

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 closedir() clarifies that if a file descriptor is used for the directory stream, it is mandatory that closedir() 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.

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 a priori 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.

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 dirp value or a dirent structure value after a directory stream has been closed or after a fork() or one of the exec function calls.  

FUTURE DIRECTIONS

None.  

SEE ALSO

closedir() , lstat() , readdir() , rewinddir() , symlink() , the Base Definitions volume of IEEE Std 1003.1-2001, <dirent.h>, <limits.h>, <sys/types.h>  

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 .


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
EXAMPLES
Open a Directory Stream
APPLICATION USAGE
RATIONALE
FUTURE DIRECTIONS
SEE ALSO
COPYRIGHT

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Time: 21:51:46 GMT, April 16, 2011