如何设置整数的前三个字节?在C ++中 [英] How to set first three bytes of integer? in C++

问题描述

我想在C ++中将整数的前三个字节设置为0.我尝试了这段代码，但是我的整数变量a并没有改变，输出始终为-63.我在做什么错了?

I want to set first three bytes of an integer to 0 in C++. I tried this code, but my integer variable a is not changing, output is always -63. What am I doing wrong?

#include <iostream>
#include <string>

int main()
{
  int a = 4294967233;
  std::cout << a << std::endl;
  for(int i = 0; i< 24; i++)
    {
        a |= (0 << (i+8));
        std::cout <<  a << std::endl;
    }

}

推荐答案

只需使用按位和(&)带掩码，就没有循环的理由:

Just use bitwise and (&) with a mask, there is no reason for loop:

a &= 0xFF000000; // Drops all but the third lowest byte
a &= 0x000000FF; // Drops all but the lowest byte

(感谢@JSF进行更正)

(Thanks to @JSF for the corrections)

如@black所述，您可以使用数字分隔符，因为C ++ 14，以使您的代码更具可读性:

As noted by @black, you may use Digit separators since C++14 in order to make your code more readable:

a &= 0xFF'00'00'00; // Drops all but the third lowest byte
a &= 0x00'00'00'FF; // Drops all but the lowest byte

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