题解 | #整数与IP地址间的转换#

#include <iostream>
#include <sstream>
#include <string>
#include <bitset>
using namespace std;
unsigned IptoDe(string ip)
{
    unsigned ipn = 0;
    int seg = 3;//控制左移位数
    istringstream iss(ip);
    while (getline(iss, ip, '.'))//分段读取十进制字符
    {
        ipn += stoi(ip) <<  8 * seg;//每段字符转换成十进制整数，再经过位运算
        --seg;
    }
    return ipn;
}
string DetoIp(unsigned ipn)
{
    string str;
    string rstr;
    str = bitset<32>(ipn).to_string();//输入先变换成二进制字符串
    for (int i = 0; i < str.size(); i += 8)//每8位字符分成一个子串
    {
        rstr += to_string(stoi(str.substr(i, 8), nullptr, 2)); //将子串转换成十进制字符串
        rstr += '.';//加入'.'分隔
    }
    rstr = rstr.substr(0, rstr.size() - 1);//去除多出的一个'.'
    return rstr;
}
int main() {
    //输入
    string ip;
    unsigned ipn;//注意ip地址是32位，unsigned int范围刚好合适
    getline(cin, ip);//点分ip读入字符串
    cin >> ipn;//整数ip读入unsigned整数
    //变换并输出
    cout << IptoDe(ip) << endl;
    cout << DetoIp(ipn) << endl;
    return 0;
}