__attribute__ 可以设置函数属性（Function Attribute ）、变量属性（Variable Attribute ）和类型属性（Type Attribute ）
aligned:
struct S
{
short b[3];
}__attribute__ ((aligned (2)));
int main()
{
struct S s;
printf("size = %lu\n",sizeof(s));
return 0;
}
aligned (n) :n必须的2的幂
结果： aligned (2) sizeof(s)= 6
aligned (4) sizeof(s)= 8
aligned (16) sizeof(s)= 16
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原文：https://www.cnblogs.com/xpylovely/p/11265579.html