c - 按位左移意外结果

Question

当我尝试左移 32 次时，我发现了一些连线问题。测试函数中的代码应该打印 0x0 的相同结果，但我得到的是“ffffffff，0”。任何人都可以提示代码有什么问题？谢谢!

int test(int n) {
    int mask = ~0 << (32 + ~n + 1);
    int mask1 = ~0 << (32 + ~0 + 1);
    printf("%x, %x\n", mask, mask1);
    return mask;
}

int main(){
    test(0);
}

Answer 1

在 C 中，移动大小大于类型大小(在您的情况下为 int)是未定义的行为

从这里topic : 相关引用自 ISO C99 (6.5.7/4)

The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with zeros. If E1 has an unsigned type, the value of the result is E1 × 2^E2, reduced modulo one more than the maximum value representable in the result type. If E1 has a signed type and nonnegative value, and E1 × 2^E2 is representable in the result type, then that is the resulting value; otherwise, the behavior is undefined.