c - 存储负数

Question

在下面这段代码中

int main()
{
int  a = -1;
printf("%d",a>>1);
return 0;
}

为什么输出 -1。

Answer 1

位移仅在无符号类型上定义，对于有符号类型，它是实现定义的。这是 R.. 的有用改进。

Strictly speaking, it is defined for signed types whenever the value is positive and the result does not overflow, and right shift is implementation-defined for negative values. Left shift, on the other hand, is undefined for negative values

┌───┬──────────────┬──────────────────────────────────┬────────────────────────┐
│   │ Unsigned     │ Signed, positive                 │ Signed, negative       │
├───┼──────────────┼──────────────────────────────────┼────────────────────────┤
│<< │ well-defined │ well-defined, except on overflow │ undefined behaviour    │
│>> │ well-defined │ well-defined                     │ implementation-defined │
└───┴──────────────┴──────────────────────────────────┴────────────────────────┘