第7章 因特网

#include <iostream>
#include <string>
#include <map>
using namespace std;

// 极简路由表：目标网络 -> 下一跳（真实情况用最长前缀匹配，这里示意查表）
string route(const map<string,string>& table, const string& dest, const string& def) {
    auto it = table.find(dest);
    return it != table.end() ? it->second : def;
}

int main() {
    map<string,string> tbl = {
        {"192.168.1.0", "eth0(直连)"},
        {"10.0.0.0",    "192.168.1.1(网关A)"},
        {"172.16.0.0",  "192.168.1.2(网关B)"}
    };
    cout << "到 10.0.0.5 经: "  << route(tbl, "10.0.0.0", "丢弃")        << "\n";
    cout << "到 8.8.8.8  经: "  << route(tbl, "8.8.8.8",  "默认路由 0.0.0.0") << "\n";
    return 0;
}

#include <iostream>
#include <string>
#include <map>
using namespace std;

// 用 map 模拟 DNS：域名 -> IP（真实 DNS 还需递归/迭代查询，这里只示意查表）
string dnsLookup(const map<string,string>& dns, const string& domain) {
    auto it = dns.find(domain);
    return it != dns.end() ? it->second : "(解析失败)";
}

int main() {
    map<string,string> dns = {
        {"www.example.com", "93.184.216.34"},
        {"www.baidu.com",   "110.242.68.66"},
        {"mail.example.com", "93.184.216.35"}
    };
    cout << "www.baidu.com -> " << dnsLookup(dns, "www.baidu.com") << "\n";
    // 真实流程：本地 DNS 先查缓存/本机 hosts，未命中再向上级(根->顶级->权威)递归查询
    return 0;
}

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

// 按 '.' 拆分域名层级（从右到左：顶级/二级/三级...）
vector<string> splitLevels(const string& domain) {
    vector<string> v; string tok;
    stringstream ss(domain);
    while (getline(ss, tok, '.')) v.push_back(tok);
    return v;
}

// 判断顶级域名类别（国家/通用/国际）
string tldType(const string& tld) {
    if (tld == "cn" || tld == "us" || tld == "uk" || tld == "jp" || tld == "hk" || tld == "tw")
        return "国家顶级域名";
    if (tld == "int") return "国际顶级域名";
    if (tld == "com" || tld == "edu" || tld == "gov" || tld == "net" || tld == "org" || tld == "mil")
        return "通用顶级域名";
    return "其他";
}

int main() {
    string d = "www.tsinghua.edu.cn";
    vector<string> lv = splitLevels(d);
    string tld = lv.back();
    cout << d << " 共 " << lv.size() << " 级，顶级域=" << tld
         << "，类别=" << tldType(tld) << "\n";  // 国家顶级域名
    return 0;
}

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

// 根据 URL 的协议头判断因特网服务类型
string serviceOf(const string& url) {
    if (url.rfind("http://", 0) == 0 || url.rfind("https://", 0) == 0) return "WWW(万维网)";
    if (url.rfind("ftp://", 0) == 0)   return "FTP(文件传输)";
    if (url.rfind("telnet://", 0) == 0) return "Telnet(远程登录)";
    return "未知服务";
}

int main() {
    cout << "http://www.baidu.com  -> " << serviceOf("http://www.baidu.com") << "\n";
    cout << "ftp://mirror/site/file -> " << serviceOf("ftp://mirror/site/file") << "\n";
    cout << "telnet://host          -> " << serviceOf("telnet://host") << "\n";
    return 0;
}

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

// 解析 URL：拆出 协议 / 主机 / 路径
void parseUrl(const string& url, string& proto, string& host, string& path) {
    size_t p = url.find("://");
    proto = url.substr(0, p);
    string rest = url.substr(p + 3);
    size_t s = rest.find('/');
    if (s == string::npos) { host = rest; path = "/"; }
    else { host = rest.substr(0, s); path = rest.substr(s); }
}

// 从一段 HTML 中提取第一个超链的 href（教学示意）
string firstHref(const string& html) {
    size_t a = html.find("href=\"");
    if (a == string::npos) return "(无超链)";
    size_t b = html.find('"', a + 6);
    return html.substr(a + 6, b - (a + 6));
}

int main() {
    string u = "https://www.example.com/docs/index.html";
    string proto, host, path;
    parseUrl(u, proto, host, path);
    cout << "协议=" << proto << " 主机=" << host << " 路径=" << path << "\n";

    string html = "<a href=\"https://www.baidu.com\">百度</a>";
    cout << "超链指向: " << firstHref(html) << "\n";
    return 0;
}

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

// 教学版邮箱合法性校验：必须含一个 '@'，前后非空，且域名含 '.'
bool validEmail(const string& s) {
    size_t at = s.find('@');
    if (at == string::npos || at == 0 || at + 1 >= s.size()) return false;
    string local  = s.substr(0, at);
    string domain = s.substr(at + 1);
    return !local.empty() && !domain.empty() && domain.find('.') != string::npos;
}

// 拆分 用户名 @ 域名
void splitMail(const string& s, string& user, string& domain) {
    size_t at = s.find('@');
    user   = s.substr(0, at);
    domain = s.substr(at + 1);
}

int main() {
    string m = "alice@example.com";
    cout << m << " 合法? " << (validEmail(m) ? "是" : "否") << "\n";
    string u, d; splitMail(m, u, d);
    cout << "用户名=" << u << " 域名=" << d << "\n";  // alice / example.com
    return 0;
}