readdir_r(3C) (man pages section 3: Basic Library Functions)

man pages section 3: Basic Library Functions

readdir_r(3C)

NAME

readdir, readdir_r– read directory

SYNOPSIS

#include <sys/types.h>
#include <dirent.h>

dirp

entry

POSIX

cc [ flag ... ] file ... -D_POSIX_PTHREAD_SEMANTICS [ library ... ]

dirp

entry

result

DESCRIPTION

The type DIR, which is defined in the header <dirent.h>, represents a directory stream, which is an ordered sequence of all the directory entries in a particular directory. Directory entries represent files; files may be removed from a directory or added to a directory asynchronously to the operation of readdir() and readdir_r().

`readdir()`

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.

`readdir_r()`

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.

RETURN VALUES

Upon successful completion, readdir() and readdir_r() return a pointer to an object of type struct dirent. When an error is encountered, a null pointer is returned and errno is set to indicate the error. When the end of the directory is encountered, a null pointer is returned and errno is not changed. The POSIX readdir_r() returns 0 if successful or an error number to indicate failure.

ERRORS

The readdir() function will fail if:

EOVERFLOW: One of the values in the structure to be returned cannot be represented correctly.

The readdir() and readdir_r() functions will fail if:

EBADF: The file descriptor determined by the DIR stream is no longer valid. This results if the DIR stream has been closed.
ENOENT: The current file pointer for the directory is not located at a valid entry.

The readdir() and readdir_r() functions may fail if:

EBADF: The dirp argument does not refer to an open directory stream.
ENOENT: The current position of the directory stream is invalid.

USAGE

The readdir() function should be used in conjunction with opendir(), closedir(), and rewinddir() to examine the contents of the directory. As readdir() returns a null pointer both at the end of the directory and on error, an application wishing to check for error situations should set errno to 0, then call readdir(), then check errno and if it is non-zero, assume an error has occurred.

Applications wishing to check for error situations should set errno to 0 before calling readdir(). If errno is set to non-zero on return, an error occurred.

The readdir() and readdir_r() functions have transitional interfaces for 64-bit file offsets. See lf64(5).

EXAMPLES

Example 1 Search the current directory for the entry `name`.

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;

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
MT-Level	See `NOTES` below.

NOTES

When compiling multithreaded programs, see Intro(3), Notes On Multithreaded Applications.

The readdir() function is unsafe in multithreaded applications. The readdir_r() function is safe, and should be used instead.

Solaris 2.4 and earlier releases provided a readdir_r() interface as specified in POSIX.1c Draft 6. The final POSIX.1c standard changed the interface as described above. Support for the Draft 6 interface is provided for compatibility only and may not be supported in future releases. New applications and libraries should use the POSIX standard interface.

For POSIX.1c-compliant applications, the _POSIX_PTHREAD_SEMANTICS and _REENTRANT flags are automatically turned on by defining the _POSIX_C_SOURCE flag with a value >= 199506L.