directory(3C)

NAME

directory, opendir, readdir, telldir, seekdir, rewinddir, closedir − directory operations

SYNOPSIS

#include <dirent.h>

DIR ∗opendir(const char ∗filename);

struct dirent ∗readdir(DIR ∗dirp);

long telldir(DIR ∗dirp);

void seekdir(DIR ∗dirp, long loc);

void rewinddir(DIR ∗dirp);

int closedir(DIR ∗dirp);

DESCRIPTION

opendir() opens the directory named by filename and associates a directory stream with it. opendir() returns a pointer to be used to identify the directory stream in subsequent operations. The directory stream is positioned at the first entry. A null pointer is returned if filename cannot be accessed or is not a directory, or if it cannot malloc(3C) enough memory to hold a DIR structure or a buffer for the directory entries.

readdir() returns a pointer to a structure representing the directory entry at the current position in the directory stream to which dirp refers, and positions the directory stream at the next entry, except on read-only filesystems. It returns a NULL pointer upon reaching the end of the directory stream, or upon detecting an invalid location in the directory. readdir() shall not return directory entries containing empty names. It is unspecified whether entries are returned for dot or dot-dot. The pointer returned by readdir() points to data that may be overwritten by another call to readdir() on the same directory stream. This data shall not be overwritten by another call to readdir() on a different directory stream. readdir() may buffer several directory entries per actual read operation; readdir() marks for updata the st_atime field of the directory each time the directory is actually read.

telldir() returns the current location associated with the named directory stream.

seekdir() sets the position of the next readdir() operation on the directory stream. The new position reverts to the position associated with the directory stream at the time the telldir() operation that provides loc was performed. Values returned by telldir() are good only for the lifetime of the DIR pointer from which they are derived. If the directory is closed and then reopened, the telldir() value may be invalidated due to undetected directory compaction. It is safe to use a previous telldir() value immediately after a call to opendir() and before any calls to readdir.

rewinddir() resets the position of the named directory stream to the beginning of the directory. It also causes the directory stream to refer to the current state of the corresponding directory, as a call to opendir() would.

closedir() closes the named directory stream and frees the DIR structure.

RETURN VALUES

opendir() and readdir() return NULL on failure and set errno to indicate the error. telldir(), seekdir(), and closedir() return −1 on failure and set errno to indicate the error.

ERRORS

opendir() will fail if one or more of the following are true:

EACCES Read permission is denied on the specified directory.

EFAULT filename points outside the allocated address space.

ELOOP Too many symbolic links were encountered in translating filename.

ENOTDIR A component of filename is not a directory.

EMFILE The maximum number of file descriptors are currently open.

ENFILE The system file table is full.

ENAMETOOLONG The length of the filename argument exceeds {PATH_MAX}, or the length of a filename component exceeds {NAME_MAX} while {_POSIX_NO_TRUNC} is in effect.

ENOENT A component of filename does not exist or is a null pathname.

EACCES A component of filename denies search permission.

readdir() will fail if one or more of the following are true:

EAGAIN Mandatory file/record locking was set, O_NDELAY or O_NONBLOCK was set, and there was a blocking record lock.

EAGAIN Total amount of system memory available when reading using raw I/O is temporarily insufficient.

EAGAIN No data is waiting to be read on a file associated with a tty device and O_NONBLOCK was set.

EAGAIN No message is waiting to be read on a stream and O_NDELAY or O_NONBLOCK was set.

EBADF The file descriptor determined by the DIR stream is no longer valid. This results if the DIR stream has been closed.

EBADMSG Message waiting to be read on a stream is not a data message.

EDEADLK The read() was going to go to sleep and cause a deadlock to occur.

EFAULT buf points to an illegal address.

EINTR A signal was caught during the read() or readv() function.

EINVAL Attempted to read from a stream linked to a multiplexor.

EIO A physical I/O error has occurred, or the process is in a background process group and is attempting to read from its controlling terminal, and either the process is ignoring or blocking the SIGTTIN signal or the process group of the process is orphaned.

ENOENT The current file pointer for the directory is not located at a valid entry.

ENOLCK The system record lock table was full, so the read() or readv() could not go to sleep until the blocking record lock was removed.

ENOLINK fildes is on a remote machine and the link to that machine is no longer active.

ENXIO The device associated with fildes is a block special or character special file and the value of the file pointer is out of range.

telldir(), seekdir(), and closedir() return 0 on success and will fail if one or more of the following are true:

EBADF The file descriptor determined by the DIR stream is no longer valid. This results if the DIR stream has been closed.

EXAMPLES

Here is a sample program that prints the names of all the files in the current directory:

#include <stdio.h>
#include <dirent.h>
main()
{
DIR ∗dirp;
struct dirent ∗direntp;
dirp = opendir( "." );
while ( (direntp = readdir( dirp )) != NULL )
(void)printf( "%s\n", direntp−>d_name );
(void)closedir( dirp );
return (0);
}

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