Significance of do ... while (0)

[krishna]

Hi all,

   Can any one explain the importance of do  ... while (0)

Regards,
Krishna Chaitanya

#define STATS_SET_HIGH(x)       do { if ((x)->num_active > (x)->high_mark) \
                                       (x)->high_mark = (x)->num_active; \
                               } while (0)
#define STATS_INC_ERR(x)        ((x)->errors++)
#define STATS_SET_FREEABLE(x, i) \
                               do { if ((x)->max_freeable < i) \
                                       (x)->max_freeable = i; \
                               } while (0)
                                                                                                                             

#define STATS_INC_ALLOCHIT(x)   atomic_inc(&(x)->allochit)
#define STATS_INC_ALLOCMISS(x)  atomic_inc(&(x)->allocmiss)
#define STATS_INC_FREEHIT(x)    atomic_inc(&(x)->freehit)
#define STATS_INC_FREEMISS(x)   atomic_inc(&(x)->freemiss)
#else
#define STATS_INC_ACTIVE(x)     do { } while (0)
#define STATS_DEC_ACTIVE(x)     do { } while (0)
#define STATS_INC_ALLOCED(x)    do { } while (0)
#define STATS_INC_GROWN(x)      do { } while (0)
#define STATS_INC_REAPED(x)     do { } while (0)
#define STATS_SET_HIGH(x)       do { } while (0)
#define STATS_INC_ERR(x)        do { } while (0)
#define STATS_SET_FREEABLE(x, i) \
                               do { } while (0)
                                                                                                                             

#define STATS_INC_ALLOCHIT(x)   do { } while (0)
#define STATS_INC_ALLOCMISS(x)  do { } while (0)
#define STATS_INC_FREEHIT(x)    do { } while (0)
#define STATS_INC_FREEMISS(x)   do { } while (0)

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