c - 它如何使输出 "fffffffe"？

Question

已关闭。此问题需要 debugging details 。目前不接受答案。

---

编辑问题以包含 desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem 。这将有助于其他人回答问题。

已关闭 7 年前。

Improve this question

这个程序如何产生以下输出？节目

#include<stdio.h>
int main()
{
printf("%x", -1<<1);
getchar();
return 0;
}

输出

fffffffe

Answer 1

C 中未定义负符号整数值的左移。

6.5.7 Bitwise shift operators

4. The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled withzeros. If E1 has an unsigned type, the value of the result is E1 × 2 E2 , reduced moduloone more than the maximum value representable in the result type. If E1 has a signedtype and nonnegative value, and E1 × 2 E2 is representable in the result type, then that isthe resulting value; otherwise, the behavior is undefined.

在您的情况下，-1 的类型是signed int。您看到的结果没有意义，而是架构的产物。