c - why 'Sizeof' value differs from the number of bytes before the flexible-length member of a struct? -

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typedef struct {  /*has 15 pointers*/ // ==> 15 x 4 = 60 bytes ;  uint16_t;           // ==>           2 bytes  uint16_t array[]; } dummy_struct;

case-a) sizeof(dummy_struct) returns 64 bytes

case-b) while if try print,

((int) &(((dummy_struct *)(0))->array[0])) prints 62 bytes.

this prints 62 bytes well: ((int) &(((dummy_struct *)(0))->array))

i don't understand why there change in value? shouldn't sizeof() return 62 well?

if there's padding of 2 bytes, shouldn't happen before flexible-length member in struct? if that's case, shouldn't case-b print 64 instead of 62?

edit:

typedef struct {     uint32_t temp;     uint8_t array[][6]; } dummy2;          printf("%d %d\n", sizeof(dummy2), offsetof(dummy2, array));  // prints 4 4          printf("%d \n",((int) &(((dummy2 *)(0))->array[0])));   // prints 4

how come same effect not happening previous example? padding doesn't seem happen here. so, possible reason previous example padding happening after flexible-size member?

the sizeof returns size of entire structure, while other 2 expressions return offset of array member, happens 2 bytes before end of struct. can same result offsetof, this:

offsetof(dummy_struct, array) // 62

demo on ideone.


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