题解 | #整数与IP地址间的转换#

#include <cstdlib>
#include <iostream>
using namespace std;

long ip2long(const string& ip)
{
    const char* s = ip.c_str();
    char* endptr = nullptr;
    long value = 0;
    for (int i = 0; i < 4; ++i) {
        auto v = strtol(s, &endptr, 10);
        s = endptr + 1;
        value = (value << 8) + v;
    }
    return value;
}

string long2ip(const long value)
{
    int c1 = value >> 24;
    int c2 = (value >> 16) & 0xFF;
    int c3 = (value >> 8) & 0xFF;
    int c4 = value & 0xFF;
    char ip[16] = {'\0'};
    snprintf(ip, sizeof(ip), "%d.%d.%d.%d", c1, c2, c3, c4);
    return string{ip};
}

int main() {
    string ip;
    long value;
    while (cin >> ip >> value) {
        cout << ip2long(ip) << endl;
        cout << long2ip(value) << endl;
    }
}
// 64 位输出请用 printf("%lld")