c struct bitfield (結構體位域)

兩篇非常棒的文章。

1. 再談c語言位域

2. Section bitfields

簡要總結一下：

C99 guarentees that bit-fields will be packed as tightly as possible, provided they don’t cross storage unit boundaries

Note that the base type of a bit field is interpreted for signedness but not necessarily for size. It is up to implementors whether "short flip:1" or "long flip:1" are supported, and whether those base types change the size of the storage unit the field is packed into.就是說int a:2;並不是說就會分配int大小的空間，可能只分配可以容納2bits的空間。

大小端不僅影響byte order，也影響bit order。

對於一個byte，定義它的各個位爲：b7 b6 b5 b4 b3 b2 b1 b0. 其中 b7 是起始地址開始的地方。