[Bug c++/37119] sizeof simple struct consisting of bit-fields too large and unpredictable

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2008-08-13 21:26 -------
>  struct X { uint32_t a:17; uint8_t b:8; bool c:1; };
0...16 is a as uint32_t is more than 17 bytes
17...24 is b as uint8_t is 8 bytes
25...26 is c as bool is 1 byte

so 26bits which is a little over 4 bytes. so it needs to be rounded (aligned)
to 4 byte so we get 8 bytes.

I don't see what the issue here is.  if we replace uint32_t with uint16_t, the
sizes are reduced as it only stores 16 bytes and the alignment of the struct
becomes 2 byte aligned.

Why do you think the original struct should be 4 bytes?  I cannot count how it
could ever be 4 bytes really except for replacing of uint32_t with uint16_t.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37119