The readdir() function returns a pointer to a structure representing the directory entry at the current position in the directory stream specified by the argument dirp, and positions the directory stream at the next entry. It returns a null pointer upon reaching the end of the directory stream. The structure dirent defined by the <dirent.h> header describes a directory entry.

If entries for . (dot) or .. (dot-dot) exist, one entry will be returned for dot and one entry will be returned for dot-dot; otherwise they will not be returned.

The pointer returned by readdir() points to data which may be overwritten by another call to readdir() on the same directory stream. This data is not overwritten by another call to readdir() on a different directory stream.

If a file is removed from or added to the directory after the most recent call to opendir(3C) or rewinddir(3C), whether a subsequent call to readdir() returns an entry for that file is unspecified.

The readdir() function may buffer 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.

After a call to fork(2), either the parent or child (but not both) may continue processing the directory stream using readdir(), rewinddir() or seekdir(3C). If both the parent and child processes use these functions, the result is undefined.

If the entry names a symbolic link, the value of the d_ino member is unspecified.

The readdir_r() function initializes the dirent structure referenced by entry to represent the directory entry at the current position in the directory stream referred to by dirp, and positions the directory stream at the next entry.

The caller must allocate storage pointed to by entry to be large enough for a dirent structure with an array of char d_name member containing at least NAME_MAX (that is, pathconf(_PC_NAME_MAX)) plus one elements. _PC_NAME_MAX is defined in <unistd.h>.

The readdir_r() function will not return directory entries containing empty names. It is unspecified whether entries are returned for . (dot) or .. (dot-dot).

If a file is removed from or added to the directory after the most recent call to opendir() or rewinddir(), whether a subsequent call to readdir_r() returns an entry for that file is unspecified.

The readdir_r() function may buffer several directory entries per actual read operation; the readdir_r() function marks for update the st_atime field of the directory each time the directory is actually read.

The POSIX version (see standards(5)) of the readdir_r() function initializes the structure referenced by entry and stores a pointer to this structure in result. On successful return, the pointer returned at *result will the same value as the argument entry. Upon reaching the end of the directory stream, this pointer will have the value NULL.

The following sample code will search the current directory for the entry name:

dirp = opendir("."); while (dirp) { errno = 0; if ((dp = readdir(dirp)) != NULL) { if (strcmp(dp->d_name, name) == 0) { closedir(dirp); return FOUND; } } else { if (errno == 0) { closedir(dirp); return NOT_FOUND; } closedir(dirp); return READ_ERROR; } } return OPEN_ERROR;