dirent, dirent64

Data structure for a directory entry

Synopsis:

#include <dirent.h>

struct dirent {
#if _FILE_OFFSET_BITS - 0 == 64
    ino_t           d_ino;     /* File serial number. */
    off_t           d_offset;
#elif !defined(_FILE_OFFSET_BITS) || _FILE_OFFSET_BITS == 32
#if defined(__LITTLEENDIAN__)
    ino_t           d_ino;     /* File serial number. */
    ino_t           d_ino_hi;
    off_t           d_offset;
    off_t           d_offset_hi;
#elif defined(__BIGENDIAN__)
    ino_t           d_ino_hi;
    ino_t           d_ino;     /* File serial number. */
    off_t           d_offset_hi;
    off_t           d_offset;
#else
 #error endian not configured for system
#endif
#else
 #error _FILE_OFFSET_BITS value is unsupported
#endif
    int16_t             d_reclen;
    int16_t             d_namelen;
    char                d_name[1];
};

struct dirent64 {
	ino64_t				d_ino;
	off64_t				d_offset;
	_Int16t				d_reclen;
	_Int16t				d_namelen;
	char				d_name[1];
};

Description:

The dirent structure describes an entry in a directory. The members include:

d_ino
A mountpoint-unique file serial number. This serial number is often used in various disk-checking utilities for such operations as determining infinite-loop directory links. (Note that the inode value cannot be zero, which would indicate that the inode represents an unused entry.)
d_offset
In some filesystems, this member identifies the directory entry itself; in others, it's the offset of the next directory entry. For a disk-based filesystem, this value might be the actual offset into the on-disk directory structure.
d_reclen
The size of this directory entry and any other associated information (such as an optional struct stat structure appended to the struct dirent entry).
d_namelen
The size of the d_name member. Since the size is calculated using strlen(), the \0 string terminator, which must be present, isn't counted.
d_name
The actual name of that directory entry.
These structures include space only for the first four bytes of the pathname. If you create an instance of this structure, you must provide space for the name, including the terminating null character: 
struct dirent *entry;
entry = malloc( offsetof(struct dirent, d_name) + NAME_MAX + 1 );

or: 

struct {
    struct dirent ent;
    char namebuf[NAME_MAX + 1 + offsetof(struct dirent, d_name) -
                 sizeof( struct dirent)];
} entry

Classification:

dirent is POSIX 1003.1; dirent64 is Large-file support

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