C++位操作符总结

#include <stdio.h>
#include <memory.h>
#include <malloc.h>
#define MaxBinLength 16

//获取无符号数的二进制，这是我自己写的，更简单的方法可以用bitset代替
char* getUnsignedBinary(unsigned int num)
{
    int len = MaxBinLength -1;
    char *bin = (char*)malloc((MaxBinLength + 1)*sizeof(char));
    memset(bin,'0',MaxBinLength);
    bin[MaxBinLength] = 0;
    while(num/2 != 0){
        bin[len--] = '0' + num%2;
        num/=2;
    }
    if(num!=0)
        bin[len--] = '1';
    return bin;
}

void flip(unsigned short num)
{
    printf("位求反,运算符为 ~ ,功能简单,将操作数的每一个二进制位取反
");
    printf("原值:%6d %s
",num,getUnsignedBinary(num));
    printf("新值:%6d %s
",~num,getUnsignedBinary(~num));
    printf("-------------------------
");
}

void left_shift(unsigned short num,unsigned short offset)
{
    printf("左移运算,运算符为 << ,将操作数的二进制位向左移动指定的offset(%d)位数,offset必须小于原数的位数,右边新加的位以0填充
",offset);
    printf("原值:%6d %s
",num,getUnsignedBinary(num));
    printf("新值:%6d %s
",num<<offset,getUnsignedBinary(num<<offset));
    printf("-------------------------
");
}

void right_shift(unsigned short num,unsigned short offset)
{
    printf("右移运算,运算符为 >> ,将操作数的二进制位向右移动指定的offset(%d)位数,offset必须小于原数的位数,

如果操作数无符号,左边新加的位以0填充,如果操作数有符号,右边新加的位可能以符号位填充，也可能以0填充,

具体依赖于机器,见注释
",offset);
    printf("原值:%6d %s
",num,getUnsignedBinary(num));
    printf("新值:%6d %s
",num>>offset,getUnsignedBinary(num>>offset));
    printf("-------------------------
");
}

void weiyu(unsigned short num,unsigned short num_1)
{
    printf("位与,运算符为 & ,对两个操作数的每一个对应二进制位进行'与'运算,运算方式类似于&&运算
");
    printf("原值:%6d %s
",num,getUnsignedBinary(num));
    printf("原值:%6d %s
",num_1,getUnsignedBinary(num_1));
    printf("新值:%6d %s
",num&num_1,getUnsignedBinary(num&num_1));
    printf("-------------------------
");
}

void weihuo(unsigned short num,unsigned short num_1)
{
    printf("位或,运算符为 | ,对两个操作数的每一个对应二进制位进行'或'运算,运算方式类似于||运算
");
    printf("原值:%6d %s
",num,getUnsignedBinary(num));
    printf("原值:%6d %s
",num_1,getUnsignedBinary(num_1));
    printf("新值:%6d %s
",num|num_1,getUnsignedBinary(num|num_1));
    printf("-------------------------
");
}

void weiyihuo(unsigned short num,unsigned short num_1)
{
    printf("位异或,运算符为 ^ ,对两个操作数的每一个对应二进制位进行'异或'运算,两个位不同则为1，相同则为0
");
    printf("原值:%6d %s
",num,getUnsignedBinary(num));
    printf("原值:%6d %s
",num_1,getUnsignedBinary(num_1));
    printf("新值:%6d %s
",num^num_1,getUnsignedBinary(num^num_1));
    printf("-------------------------
");
}

void zhushi()
{
    printf("注释:位操作符只能操作整数,这个整数可以是有符号的也可以是无符号的,

如果操作数为负数,则位如何处理其符号位依赖于机器,所以在一个环境中实现的

程序可能无法用于另一环境，因此强烈建议使用unsigned整数作为操作数

参考<<C++primer>>(人民邮电出版社第4版)155页
");
    printf("-------------------------
");
}

int main()
{
    unsigned short num = 125,num_1 = 26,offset = 3;
    flip(num);
    left_shift(num,offset);
    right_shift(num,offset);
    weiyu(num,num_1);
    weihuo(num,num_1);
    weiyihuo(num,num_1);
    zhushi();
    return 0;
}

 后来又自己试了一下，当在左移运算中，offset是可以大于操作数的长度的。当offset大一操作数长度的时候，操作的结果会自动更改整数类型，以容纳更多的位数,例如unsigned char可以变为short，short可以变为int等。

而右移运算中，无论offset为何值,操作结果的长度不会发证变化。

看demo，只是经过简单的验证。

#include <bitset>
#include <iostream>
#include <iomanip>
using namespace std;

#define uint8_t unsigned char 
#define uint16_t unsigned short
#define uint32_t unsigned int

bitset<32> getBinary32(int num)
{
    bitset<32> bit(num);
    return bit;
}

bitset<8> getBinary8(uint8_t num)
{
    bitset<8> bit(num);
    return bit;
}


int main()
{
    uint8_t a = 255;
    //左移
    cout<<"左移"<<endl<<"a="<<(int)a<<" "<<getBinary8(a)<<endl;
    for(int i = 0;i<=24;i++)
    {
        if(i < 8)
        {
            uint16_t b = a<<i;
            cout<<"b="<<setw(10)<<(unsigned short)b<<" "<<getBinary32(b)<<endl;
        }
        else
        {
            uint32_t b = a<<i;
            cout<<"b="<<setw(10)<<(unsigned int)b<<" "<<getBinary32(b)<<endl;
        }
    }

    //右移
    cout<<"右移"<<endl<<"a="<<(int)a<<" "<<getBinary8(a)<<endl;
    for(i = 0;i<=24;i++)
    {
        if(i < 8)
        {
            uint16_t b = a>>i;
            cout<<"b="<<setw(10)<<(unsigned short)b<<" "<<getBinary32(b)<<endl;
        }
        else
        {
            uint32_t b = a>>i;
            cout<<"b="<<setw(10)<<(unsigned int)b<<" "<<getBinary32(b)<<endl;
        }
    }
    return 0;
}