swap两个数,一种类型无关.宏, 来自 kernel.h

swap.c

#define swap(a, b) \
	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)

/// 临时变量名字,
/// from http://stackoverflow.com/questions/3982348/implement-generic-swap-macro-in-c
#define swap(x, y) \
  do { typeof(x) temp##x##y = x; x = y; y = temp##x##y; } while (0)