[IRCServices Coding] GCC3

[Andrew Church]

>>      Again, that's what I thought--compilers aren't supposed to pad more
>> than the largest type in the structure, and between structure members only
>> enough to align the next member to a multiple of its size.  I'm pretty sure
>> this is defined somewhere, and if not then it should be (see below).
>Not the largest type in the structure, the largest *type*.
>Most structures will pad to 32 bits on intel machines.
>
>like this:
>
>struct {
>  int8_t byte;
>  /* inserts 8 or 24 bits of padding here */
>  int16_t word;
>  /* inserts 16 bits of padding here */
>  int32_t dword;
>  /* no padding here */
>} something;

     That's missing the point; you put a 32-bit type in there, which of
course means it will pad to 32 bits.  (And by your argument, it would have
to pad to at least the size of a double, not just an int32_t.)  What you're
saying would be something like:

struct {
    int8_t byte;
    /* 24 bits of padding */
    int16_t word;
    /* 16 bits of padding */
} foo;  /* size = 64 bits */

which is stupid because you have 32 bits of wasted space, when you could
just as easily and with no alignment problems (at least on any CPU I know
of) have done:

struct {
    int8_t byte;
    /* 8 bits of padding */
    int16_t word;
} bar;  /* size = 32 bits */

  --Andrew Church
    achurch at achurch.org
    http://achurch.org/