文件流操作

std::ifstream  fin("data.txt");      // 只读文件
std::ofstream  fout("out.txt");      // 只写文件
std::fstream   fio("data.txt", std::ios::in | std::ios::out);  // 读写

#include <iostream>
#include <fstream>
#include <string>
#include <map>
#include <sstream>

// 读写飞翔科技配置
bool readConfig(const std::string& path,
                std::map<std::string, std::string>& config) {
    std::ifstream fin(path);
    if (!fin) {
        std::cerr << "无法打开: " << path << "\n";
        return false;
    }

    std::string line;
    while (std::getline(fin, line)) {
        // 跳过空行和注释
        if (line.empty() || line[0] == '#') continue;

        auto pos = line.find('=');
        if (pos != std::string::npos) {
            std::string key = line.substr(0, pos);
            std::string val = line.substr(pos + 1);
            config[key] = val;
        }
    }
    return true;
}

bool writeConfig(const std::string& path,
                 const std::map<std::string, std::string>& config) {
    std::ofstream fout(path);
    if (!fout) return false;

    fout << "# 飞翔科技服务器配置\n";
    fout << "# 生成时间: 2026-06-14\n\n";
    for (const auto& [key, val] : config)
        fout << key << "=" << val << "\n";
    return true;
}

int main() {
    std::string configPath = "C:/Users/AOXIANG/Desktop/Cpp/指南/13_IO流与文件/feixiang.conf";

    // 1. 写入初始配置
    std::map<std::string, std::string> config = {
        {"server_name", "飞翔科技-主站"},
        {"port", "8080"},
        {"max_connections", "10000"},
        {"log_level", "INFO"},
        {"db_host", "192.168.1.100"},
    };

    if (writeConfig(configPath, config))
        std::cout << "配置已写入: " << configPath << "\n";
    else
        std::cerr << "写入失败\n";

    // 2. 读取验证
    std::map<std::string, std::string> loaded;
    if (readConfig(configPath, loaded)) {
        std::cout << "\n读取配置:\n";
        for (const auto& [k, v] : loaded)
            std::cout << "  " << k << " = " << v << "\n";
    }

    // 3. 追加模式添加新配置
    std::ofstream fout(configPath, std::ios::app);
    fout << "cache_ttl=3600\n";
    fout << "enable_monitoring=true\n";
    fout.close();
    std::cout << "\n已追加 2 条配置\n";

    // 4. 重新读取验证追加
    loaded.clear();
    readConfig(configPath, loaded);
    std::cout << "\n最终配置 (" << loaded.size() << " 项):\n";
    for (const auto& [k, v] : loaded)
        std::cout << "  " << k << " = " << v << "\n";
}

#include <iostream>
#include <fstream>
#include <cstring>
#include <vector>

// 固定长度记录，方便二进制随机访问
#pragma pack(push, 1)
struct LogIndex {
    char     timestamp[20];   // "2026-06-14 09:00:00"
    int64_t  offset;          // 日志文件中的偏移
    int32_t  length;          // 日志条目长度
    int32_t  level;           // 0=INFO, 1=WARN, 2=ERROR
};
#pragma pack(pop)

void printIndex(const LogIndex& idx) {
    std::cout << "  " << idx.timestamp
              << " | offset=" << idx.offset
              << " | len=" << idx.length
              << " | level=" << idx.level << "\n";
}

int main() {
    std::string binaryPath =
        "C:/Users/AOXIANG/Desktop/Cpp/指南/13_IO流与文件/feixiang_log.idx";

    // 1. 写入二进制索引
    std::vector<LogIndex> indices = {
        {"2026-06-14 09:00:00", 0,      256,  0},
        {"2026-06-14 09:05:12", 256,    512,  0},
        {"2026-06-14 09:10:45", 768,    128,  1},
        {"2026-06-14 09:15:33", 896,    1024, 0},
        {"2026-06-14 09:20:01", 1920,   64,   2},
    };

    {
        std::ofstream fout(binaryPath, std::ios::binary);
        if (!fout) {
            std::cerr << "无法创建文件\n";
            return 1;
        }

        fout.write(reinterpret_cast<const char*>(indices.data()),
                   indices.size() * sizeof(LogIndex));
        fout.close();
        std::cout << "二进制索引写入: " << indices.size() << " 条记录\n";
    }

    // 2. 顺序读取所有记录
    {
        std::ifstream fin(binaryPath, std::ios::binary);
        std::cout << "\n顺序读取:\n";
        LogIndex idx;
        while (fin.read(reinterpret_cast<char*>(&idx), sizeof(LogIndex)))
            printIndex(idx);
    }

    // 3. 随机访问：跳到第 3 条记录
    {
        std::ifstream fin(binaryPath, std::ios::binary);
        fin.seekg(2 * sizeof(LogIndex), std::ios::beg);  // 第3条（0-based索引2）
        LogIndex idx;
        fin.read(reinterpret_cast<char*>(&idx), sizeof(LogIndex));
        std::cout << "\n随机访问（第3条）:\n";
        printIndex(idx);

        // 获取当前读取位置
        auto pos = fin.tellg();
        std::cout << "  当前文件指针位置: " << pos << " 字节\n";
    }

    // 4. 筛选 ERROR 级别（level=2）
    {
        std::ifstream fin(binaryPath, std::ios::binary);
        std::cout << "\n筛选 ERROR 级别:\n";
        LogIndex idx;
        while (fin.read(reinterpret_cast<char*>(&idx), sizeof(LogIndex))) {
            if (idx.level == 2) printIndex(idx);
        }
    }
}

// ❌ 文本模式在 Windows 上会将 \n 转为 \r\n，破坏二进制数据
std::ofstream fout("data.bin");
fout.write(data, size);

// ✅
std::ofstream fout("data.bin", std::ios::binary);

std::ofstream fout("/root/protected/config.txt");
// 没有 if (!fout) 检查，直接写入 → 静默失败

fin.seekg(0);  // 重置位置
// fin.clear();  // 必须：seekg 不自动清除 eofbit！
std::string line;
std::getline(fin, line);  // 如果不清 eofbit 可能失败