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.  The 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 the next active directory entry and positions the directory stream at the next entry.  No inactive entries are returned.  It returns NULL upon reaching the end of the directory or upon detecting an invalid location in the directory.  The directory entry returned is valid only for the lifetime of the DIR pointer from which it is derived; the directory entry is constructed in space that is released when closedir() releases the resources associated with its view of DIR.  readdir buffers several directory entries per actual read operation; readdir marks for update 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 directory stream at the time the telldir operation that provides loc was performed.  Values returned by telldir are valid only if the directory has not changed because of compaction or expansion.  This situation is not a problem with System V, but it may be a problem with some file system types. 

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. 

The following errors can occur as a result of these operations. 

opendir returns NULL on failure and sets errno to one of the following values:

ENOTDIR A component of filename is not a directory. 

EACCES A component of filename denies search permission. 

EACCES Read permission is denied on the specified directory. 

EMFILE The maximum number of file descriptors are currently open. 

ENFILE The system file table is full. 

EFAULT filename points outside the allocated address space. 

ELOOP Too many symbolic links were encountered in translating filename. 

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. 

readdir returns NULL on failure and sets errno to one of the following values:

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

EBADF The file descriptor determined by the DIR stream is no longer valid.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

telldir, seekdir, and  closedir return −1 on failure and set errno to the following value:

EBADF The file descriptor determined by the DIR stream is no longer valid.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

EXAMPLE

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 );
closedir( dirp );
return (0);
}

SEE ALSO

getdents(2), dirent(4)

NOTES

rewinddir is implemented as a macro, so its function address cannot be taken.