читать каталог (read a directory)
Имя (Name)
readdir - read a directory
Синопсис (Synopsis)
#include <dirent.h>
struct dirent *readdir(DIR *dirp);
Описание (Description)
The readdir() function returns a pointer to a dirent structure
representing the next directory entry in the directory stream
pointed to by dirp. It returns NULL on reaching the end of the
directory stream or if an error occurred.
In the glibc implementation, the dirent structure is defined as
follows:
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 */
};
The only fields in the dirent structure that are mandated by
POSIX.1 are d_name and d_ino. The other fields are
unstandardized, and not present on all systems; see NOTES below
for some further details.
The fields of the dirent structure are as follows:
d_ino This is the inode number of the file.
d_off The value returned in d_off is the same as would be
returned by calling telldir(3) at the current position in
the directory stream. Be aware that despite its type and
name, the d_off field is seldom any kind of directory
offset on modern filesystems. Applications should treat
this field as an opaque value, making no assumptions about
its contents; see also telldir(3).
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.
d_type This field contains a value indicating the file type,
making it possible to avoid the expense of calling
lstat(2) if further actions depend on the type of the
file.
When a suitable feature test macro is defined
(_DEFAULT_SOURCE on glibc versions since 2.19, or
_BSD_SOURCE on glibc versions 2.19 and earlier), glibc
defines the following macro constants for the value
returned in d_type:
DT_BLK This is a block device.
DT_CHR This is a character device.
DT_DIR This is a directory.
DT_FIFO
This is a named pipe (FIFO).
DT_LNK This is a symbolic link.
DT_REG This is a regular file.
DT_SOCK
This is a UNIX domain socket.
DT_UNKNOWN
The file type could not be determined.
Currently, only some filesystems (among them: Btrfs, ext2,
ext3, and ext4) have full support for returning the file
type in d_type. All applications must properly handle a
return of DT_UNKNOWN.
d_name This field contains the null terminated filename. See
NOTES.
The data returned by readdir() may be overwritten by subsequent
calls to readdir() for the same directory stream.
Возвращаемое значение (Return value)
On success, readdir() returns a pointer to a dirent structure.
(This structure may be statically allocated; do not attempt to
free(3) it.)
If the end of the directory stream is reached, NULL is returned
and errno is not changed. If an error occurs, NULL is returned
and errno is set to indicate the error. To distinguish end of
stream from an error, set errno to zero before calling readdir()
and then check the value of errno if NULL is returned.
Ошибки (Error)
EBADF Invalid directory stream descriptor dirp.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────┬───────────────┬──────────────────────────┐
│Interface │ Attribute │ Value │
├─────────────────────┼───────────────┼──────────────────────────┤
│readdir() │ Thread safety │ MT-Unsafe race:dirstream │
└─────────────────────┴───────────────┴──────────────────────────┘
In the current POSIX.1 specification (POSIX.1-2008), readdir() is
not required to be thread-safe. However, in modern
implementations (including the glibc implementation), concurrent
calls to readdir() that specify different directory streams are
thread-safe. In cases where multiple threads must read from the
same directory stream, using readdir() with external
synchronization is still preferable to the use of the deprecated
readdir_r(3) function. It is expected that a future version of
POSIX.1 will require that readdir() be thread-safe when
concurrently employed on different directory streams.
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
Примечание (Note)
A directory stream is opened using opendir(3).
The order in which filenames are read by successive calls to
readdir() depends on the filesystem implementation; it is
unlikely that the names will be sorted in any fashion.
Only the fields d_name and (as an XSI extension) d_ino are
specified in POSIX.1. Other than Linux, the 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 _DIRENT_HAVE_D_NAMLEN,
_DIRENT_HAVE_D_RECLEN, _DIRENT_HAVE_D_OFF, or _DIRENT_HAVE_D_TYPE
are defined.
The d_name field
The dirent structure definition shown above is taken from the
glibc headers, and shows the d_name field with a fixed size.
Warning: applications should avoid any dependence on the size of
the d_name field. POSIX defines it as char d_name[], a character
array of unspecified size, with at most NAME_MAX characters
preceding the terminating null byte ('\0').
POSIX.1 explicitly notes that this field should not be used as an
lvalue. The standard also notes that the use of sizeof(d_name)
is incorrect; use strlen(d_name) instead. (On some systems, this
field is defined as char d_name[1]!) By implication, the use
sizeof(struct dirent) to capture the size of the record including
the size of 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 d_name can actually exceed this
size. In such cases, the d_reclen field will contain a value
that exceeds the size of the glibc dirent structure shown above.
Смотри также (See also)
getdents(2), read(2), closedir(3), dirfd(3), ftw(3), offsetof(3),
opendir(3), readdir_r(3), rewinddir(3), scandir(3), seekdir(3),
telldir(3)
