arr[0] is kernel code ???

[Onkar <onkar.n.m@xxxxxxxxx>]

Hi All , 
       Why is 0 length arrays

for instance 

struct ext2_xattr_entry {
    __u8    e_name_len;    /* length of name */
    __u8    e_name_index;    /* attribute name index */
    __le16    e_value_offs;    /* offset in disk block of value */
    __le32    e_value_block;    /* disk block attribute is stored on (n/i) */
    __le32    e_value_size;    /* size of attribute value */
    __le32    e_hash;        /* hash value of name and value */
    char    e_name[0];    /* attribute name */ <<<-------------------------------------------- Why ??
};

AND 

struct mb_cache_entry {
    struct list_head        e_lru_list;
    struct mb_cache            *e_cache;
    unsigned short            e_used;
    unsigned short            e_queued;
    struct block_device        *e_bdev;
    sector_t            e_block;
    struct list_head        e_block_list;
    struct {
        struct list_head    o_list;
        unsigned int        o_key;
    } e_indexes[0]; <<<-------------------------------------------- Why ??
};

 used in many structures in the kernel code ? What is their significance ?  and Why is

do { 
 // exp 1
//exp 2 
//exp 3 
}while (0) ; 

used ? 

Regards, 
Onkar