第6章 计算机网络

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

int main() {
    string data = "Hello";
    // 应用层 -> 传输层(加端口头) -> 网络层(加IP头) -> 链路层(加MAC头)
    string seg   = "[TCP头:端口]" + data;
    string pkt   = "[IP头:地址]" + seg;
    string frame = "[MAC头]" + pkt + "[MAC尾]";
    cout << "最终在线路上传输的帧: " << frame << "\n";
    return 0;
}

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

// 把 48 位 MAC 整数格式化为 xx:xx:xx:xx:xx:xx
string macToStr(unsigned long long mac) {
    char buf[18];
    sprintf(buf, "%02X:%02X:%02X:%02X:%02X:%02X",
            (int)((mac >> 40) & 0xFF), (int)((mac >> 32) & 0xFF),
            (int)((mac >> 24) & 0xFF), (int)((mac >> 16) & 0xFF),
            (int)((mac >> 8) & 0xFF),  (int)(mac & 0xFF));
    return buf;
}

int main() {
    unsigned long long mac = 0x001B44113A9Dull;
    cout << "MAC 地址: " << macToStr(mac) << "\n";  // 00:1B:44:11:3A:9D
    return 0;
}

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

// 按首字节判断 IPv4 类别
string ipClass(const string& s) {
    int a; sscanf(s.c_str(), "%d.", &a);
    if (a >= 1   && a <= 126) return "A";
    if (a >= 128 && a <= 191) return "B";
    if (a >= 192 && a <= 223) return "C";
    if (a >= 224 && a <= 239) return "D(组播)";
    if (a >= 240 && a <= 255) return "E(保留)";
    return "特殊(0/127)";
}

int main() {
    cout << "10.0.0.1     -> " << ipClass("10.0.0.1")     << "\n"; // A
    cout << "172.16.0.1   -> " << ipClass("172.16.0.1")   << "\n"; // B
    cout << "192.168.1.1  -> " << ipClass("192.168.1.1")  << "\n"; // C
    return 0;
}

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

unsigned int ipToInt(const string& s) {
    int a, b, c, d; sscanf(s.c_str(), "%d.%d.%d.%d", &a, &b, &c, &d);
    return ((unsigned int)a << 24) | ((unsigned int)b << 16) |
           ((unsigned int)c << 8)  | (unsigned int)d;
}
string intToIp(unsigned int v) {
    char buf[20];
    sprintf(buf, "%u.%u.%u.%u", (v >> 24) & 0xFF, (v >> 16) & 0xFF,
            (v >> 8) & 0xFF, v & 0xFF);
    return buf;
}
unsigned int prefixToMask(int p) {
    return (p == 0) ? 0u : (0xFFFFFFFFu << (32 - p));
}

int main() {
    string ip = "192.168.1.100";
    int p = 24;
    unsigned int ipv = ipToInt(ip);
    unsigned int mask = prefixToMask(p);
    unsigned int net  = ipv & mask;
    unsigned int bcast = net | ~mask;
    unsigned int hosts = (1u << (32 - p)) - 2;

    cout << "IP:        " << intToIp(ipv) << "\n";
    cout << "掩码:      " << intToIp(mask) << "  (/ " << p << ")\n";
    cout << "网络地址:  " << intToIp(net)  << "\n";   // 192.168.1.0
    cout << "广播地址:  " << intToIp(bcast)<< "\n";   // 192.168.1.255
    cout << "可用主机数:" << hosts        << "\n";     // 254
    return 0;
}

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

string portType(int p) {
    if (p <= 1023)  return "知名/系统端口";
    if (p <= 49151) return "注册端口";
    return "动态/私有端口";
}

int main() {
    cout << "端口 80   -> " << portType(80)   << "\n";  // 知名
    cout << "端口 8080 -> " << portType(8080) << "\n";  // 注册
    cout << "端口 50000-> " << portType(50000)<< "\n";  // 动态
    return 0;
}

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

// 教学：拼接一个 HTTP/1.1 GET 请求字符串（不实际发包）
string buildGet(const string& host, const string& path) {
    return "GET " + path + " HTTP/1.1\r\n"
         + "Host: " + host + "\r\n"
         + "Connection: close\r\n\r\n";
}

int main() {
    cout << buildGet("www.example.com", "/index.html");
    return 0;
}