C++实现文本与二进制文件读写操作的示例

#include <fstream>
#include <string>

int main() {
    // 创建输出流（默认覆盖模式）
    std::ofstream outFile("data.txt");
    
    if (!outFile) {
        std::cerr << "文件创建失败！" << std::endl;
        return 1;
    }
    
    // 写入不同类型数据
    outFile << "用户日志\n";
    outFile << "ID: " << 1001 << "\n";
    outFile << "余额: $" << 2450.75 << "\n";
    
    // 自动关闭文件（RAII）
    return 0;
}

#include <fstream>
#include <iostream>

int main() {
    std::ifstream inFile("data.txt");
    
    if (!inFile.is_open()) {
        std::cerr << "文件打开失败！" << std::endl;
        return 1;
    }
    
    // 逐行读取
    std::string line;
    while (std::getline(inFile, line)) {
        std::cout << line << std::endl;
    }
    
    // 重置读取位置
    inFile.clear();
    inFile.seekg(0);
    
    // 格式化读取
    int id;
    double balance;
    inFile.ignore(100, ':');  // 跳过"ID: "
    inFile >> id;
    inFile.ignore(100, '$'); // 跳过"余额: $"
    inFile >> balance;
    
    std::cout << "\n解析结果: ID=" << id 
              << ", 余额=" << balance << std::endl;
    
    return 0;
}

#include <fstream>

struct UserData {
    int id;
    double balance;
    char name[32];
};

int main() {
    UserData user = {1001, 2450.75, "张三"};
    
    std::ofstream binFile("user.dat", std::ios::binary);
    binFile.write(reinterpret_cast<char*>(&user), sizeof(user));
    
    return 0;
}

#include <fstream>
#include <iostream>

int main() {
    std::ifstream binFile("user.dat", std::ios::binary);
    
    if (!binFile) {
        std::cerr << "二进制文件打开失败！" << std::endl;
        return 1;
    }
    
    UserData user;
    binFile.read(reinterpret_cast<char*>(&user), sizeof(user));
    
    std::cout << "用户ID: " << user.id << "\n"
              << "姓名: " << user.name << "\n"
              << "余额: " << user.balance << std::endl;
    
    return 0;
}

// 示例：以追加模式写入文本
std::ofstream logFile("app.log", 
                     std::ios::out | std::ios::app);
                     
// 示例：读写二进制文件（不截断）
std::fstream dataFile("records.dat",
                     std::ios::binary |
                     std::ios::in | 
                     std::ios::out);

std::fstream file("critical.dat");

// 检查文件状态
if (file.fail()) {
    std::cerr << "文件操作失败！" << std::endl;
}

// 详细错误诊断
if (!file) {
    if (file.bad()) {
        std::cerr << "不可恢复的错误" << std::endl;
    } else if (file.eof()) {
        std::cerr << "到达文件末尾" << std::endl;
    } else if (file.fail()) {
        std::cerr << "非致命错误（如格式错误）" << std::endl;
    }
}

{
    std::ofstream tmpFile("temp.txt");
    // 文件在作用域结束时自动关闭
}

bool copyFile(const std::string& src, const std::string& dst) {
    std::ifstream in(src, std::ios::binary);
    std::ofstream out(dst, std::ios::binary);
    
    if (!in || !out) return false;
    
    const size_t BUFFER_SIZE = 4096;
    char buffer[BUFFER_SIZE];
    
    while (in.read(buffer, BUFFER_SIZE)) {
        out.write(buffer, BUFFER_SIZE);
    }
    out.write(buffer, in.gcount());  // 写入剩余字节
    
    return true;
}

#include <filesystem>
namespace fs = std::filesystem;

// 检查文件存在
if (fs::exists("data.txt")) {
    // 获取文件大小
    auto size = fs::file_size("data.txt");
    // 重命名文件
    fs::rename("old.txt", "new.txt");
}

class Logger {
public:
    Logger(const std::string& filename) 
        : logFile(filename, std::ios::app) {}
    
    ~Logger() { if (logFile) logFile.close(); }
    
    void log(const std::string& message) {
        if (!logFile) return;
        
        auto now = std::chrono::system_clock::now();
        auto time = std::chrono::system_clock::to_time_t(now);
        logFile << std::put_time(std::localtime(&time), "%F %T")
                << " | " << message << "\n";
    }
    
private:
    std::ofstream logFile;
};

// 使用示例
Logger logger("app.log");
logger.log("系统启动");
logger.log("用户登录: ID=1001");