xref: /openbsd/lib/libc/gen/opendir.3 (revision f7d60097)

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.Dd $Mdocdate: March 23 2024 $
.Dt OPENDIR 3
.Os
.Sh NAME
.Nm opendir ,
.Nm fdopendir ,
.Nm readdir ,
.Nm readdir_r ,
.Nm telldir ,
.Nm seekdir ,
.Nm rewinddir ,
.Nm closedir ,
.Nm dirfd
.Nd directory operations
.Sh SYNOPSIS
.In sys/types.h
.In dirent.h
.Ft DIR *
.Fn opendir "const char *filename"
.Ft DIR *
.Fn fdopendir "int fd"
.Ft struct dirent *
.Fn readdir "DIR *dirp"
.Ft int
.Fn readdir_r "DIR *dirp" "struct dirent *entry" "struct dirent **result"
.Ft long
.Fn telldir "const DIR *dirp"
.Ft void
.Fn seekdir "DIR *dirp" "long loc"
.Ft void
.Fn rewinddir "DIR *dirp"
.Ft int
.Fn closedir "DIR *dirp"
.Ft int
.Fn dirfd "DIR *dirp"
.Sh DESCRIPTION
The
.Fn opendir
function opens the directory named by
.Fa filename ,
associates a directory stream with it, and returns a pointer to be used
to identify the directory stream in subsequent operations.
On failure,
.Dv NULL
is returned and
.Va errno
is set to indicate the error.
.Pp
The
.Fn fdopendir
function is equivalent to
.Fn opendir
except that the directory is specified by file descriptor rather than by name.
The file offset associated with the file descriptor at the time of the call
determines which entries are returned.
.Pp
Upon successful return from
.Fn fdopendir ,
the file descriptor is under the control of the system,
and if any attempt is made to close the file descriptor
or to modify the state of the associated directory,
other than by means of
.Fn closedir ,
.Fn readdir ,
.Fn readdir_r ,
or
.Fn rewinddir ,
the behavior is undefined.
Upon calling
.Fn closedir
the file descriptor shall be closed.
.Pp
The
.Fn readdir
function returns a pointer to the next directory entry in the named
directory stream
.Fa dirp .
It returns
.Dv NULL
upon reaching the end of the directory or detecting an invalid
.Fn seekdir
operation.
.Pp
The
.Fn readdir_r
function is a deprecated variant of
.Fn readdir .
Like
.Fn readdir ,
it initializes the
.Vt dirent
structure referenced by
.Fa entry
to represent the next directory entry in the named directory stream
.Fa dirp ,
and stores a pointer to this structure at the location referenced by
.Fa result .
The storage pointed to by
.Fa entry
must be large enough for a dirent with a
.Fa d_name
array member containing at least
.Dv NAME_MAX
plus one elements.
.Fn readdir_r
returns 0 on success, or an error number if an error occurs; see
.Sx ERRORS .
On successful return, the pointer returned at
.Fa "*result"
will have the same value as the argument
.Fa entry .
Upon reaching the end of the directory stream, this pointer shall have the value
.Dv NULL .
.Pp
The
.Fn telldir
function returns the current location associated with the named
directory stream
.Fa dirp .
On failure, \-1 is returned and
.Va errno
is set to indicate the error.
.Pp
The
.Fn seekdir
function sets the position of the next
.Fn readdir
operation on the named directory stream
.Fa dirp .
The new position reverts to the one associated with the
directory stream when the
.Fn telldir
operation was performed.
Values returned by
.Fn telldir
are good only for the lifetime of the
.Dv DIR
pointer,
.Fa dirp ,
from which they are derived.
If the directory is closed and then reopened, the
.Fn telldir
value may be invalidated due to undetected directory compaction.
.Pp
The
.Fn rewinddir
function resets the position of the named directory stream
.Fa dirp
to the beginning of the directory.
.Pp
The
.Fn closedir
function closes the named directory stream and frees the structure
associated with the
.Fa dirp
pointer, returning 0 on success.
On failure, \-1 is returned and the global variable
.Va errno
is set to indicate the error.
.Pp
The
.Fn dirfd
function returns the integer file descriptor associated with the named
directory stream
.Fa dirp
(see
.Xr open 2 ) .
.Sh EXAMPLES
Sample code which searches a directory for entry
.Dq name
is:
.Bd -literal -offset indent
len = strlen(name);
dirp = opendir(".");
if (dirp) {
	while ((dp = readdir(dirp)) != NULL)
		if (dp->d_namlen == len &&
		    !strcmp(dp->d_name, name)) {
			closedir(dirp);
			return FOUND;
		}
	closedir(dirp);
}
return NOT_FOUND;
.Ed
.Sh ERRORS
The
.Fn opendir
function will fail if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
The supplied
.Fa filename
is not a directory.
.El
.Pp
The
.Fn opendir
function may also fail and set
.Va errno
for any of the errors specified for the routines
.Xr fcntl 2 ,
.Xr fstat 2 ,
.Xr open 2 ,
and
.Xr malloc 3 .
.Pp
The
.Fn fdopendir
function will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument is not a valid file descriptor open for reading.
.It Bq Er ENOTDIR
The descriptor
.Fa fd
is not associated with a directory.
.El
.Pp
The
.Fn readdir
and
.Fn readdir_r
functions may also fail and set
.Va errno
for any of the errors specified for the routine
.Xr getdents 2 .
.Pp
The
.Fn telldir
function may also fail and set
.Va errno
for any of the errors specified for the routine
.Xr realloc 3 .
.Pp
The
.Fn closedir
function may also fail and set
.Va errno
for any of the errors specified for the routine
.Xr close 2 .
.Sh SEE ALSO
.Xr close 2 ,
.Xr getdents 2 ,
.Xr lseek 2 ,
.Xr open 2 ,
.Xr dir 5
.Sh STANDARDS
The
.Fn opendir ,
.Fn fdopendir ,
.Fn readdir ,
.Fn readdir_r ,
.Fn telldir ,
.Fn seekdir ,
.Fn rewinddir ,
.Fn closedir ,
and
.Fn dirfd
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn opendir ,
.Fn readdir ,
.Fn telldir ,
.Fn seekdir ,
.Fn rewinddir ,
.Fn closedir ,
and
.Fn dirfd
functions appeared in
.Bx 4.2 .
The
.Fn fdopendir
function appeared in
.Ox 5.0 .
.Sh CAVEATS
The
.Fn readdir_r
function was intended to provide a thread-safe version of
.Fn readdir .
However, it was later found to be both unnecessary in the typical
usage and unportable due to insufficient buffer sizing guidance.
It was therefore officially deprecated in issue 8.