题解 | 整数与IP地址间的转换

#include <iostream>
#include <bitset>
#include <vector>
#include <sstream>
using namespace std;

int main() {
    string ip_str;
    unsigned long ip_num;
    cin >> ip_str;
    cin >> ip_num;

    //ip->10进制
    stringstream ss(ip_str);
    string token;
    unsigned long decimal = 0;
    while(getline(ss, token, '.')) {
        decimal = (decimal << 8) | stoi(token);
    }

    //10进制->ip
    bitset<32> bits(ip_num);
    string ans_str;
    for(int i = 3; i >= 0; --i) {
        unsigned long tmp = (bits.to_ulong() >> (i*8)) & 0xFF;
        ans_str = ans_str + to_string(tmp) + (i ? "." : "");
    }

    cout << decimal << endl;
    cout << ans_str << endl;
    return 0;
}