Originální popis anglicky:
opendir - open a directory
Návod, kniha: POSIX Programmer's Manual
#include <dirent.h>
DIR *opendir(const char *
dirname);
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.
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.
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.
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) {
...
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.
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.
None.
closedir() ,
lstat() ,
readdir() ,
rewinddir() ,
symlink() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<dirent.h>,
<limits.h>,
<sys/types.h>
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
.
