#include <iostream>
#include <string>

int main() {
    // 标准输出
    std::cout << "Hello, World!" << std::endl;
    std::cout << "The answer is " << 42 << std::endl;
    
    // 标准输入
    int age;
    std::string name;
    std::cout << "Enter name and age: ";
    std::cin >> name >> age;
    std::cout << "Hello, " << name << "! Age: " << age << std::endl;
    
    // 读取整行
    std::string line;
    std::cout << "Enter a sentence: ";
    std::getline(std::cin, line);
    std::cout << "You said: " << line << std::endl;
    
    // 标准错误
    std::cerr << "Error: something went wrong!" << std::endl;
    std::clog << "Log: this is a log message" << std::endl;
    
    return 0;
}

#include <iostream>
#include <fstream>
#include <string>

int main() {
    // 写入文件
    std::ofstream outfile("test.txt");
    if (!outfile) {
        std::cerr << "Error opening file for writing" << std::endl;
        return 1;
    }
    outfile << "Hello, File!" << std::endl;
    outfile << "Line 2: " << 42 << std::endl;
    outfile.close();
    
    // 读取文件
    std::ifstream infile("test.txt");
    if (!infile) {
        std::cerr << "Error opening file for reading" << std::endl;
        return 1;
    }
    std::string line;
    while (std::getline(infile, line)) {
        std::cout << line << std::endl;
    }
    infile.close();
    
    // 追加模式
    std::ofstream appfile("test.txt", std::ios::app);
    appfile << "Appended line" << std::endl;
    appfile.close();
    
    // 读写模式
    std::fstream iofile("test.txt", std::ios::in | std::ios::out);
    if (iofile) {
        std::string first_line;
        std::getline(iofile, first_line);
        std::cout << "First line: " << first_line << std::endl;
        iofile.close();
    }
    
    return 0;
}

#include <iostream>
#include <sstream>
#include <string>
#include <iomanip>

int main() {
    // ostringstream：构建字符串
    std::ostringstream oss;
    oss << "Name: Alice, Age: " << 20 
        << ", Score: " << std::fixed << std::setprecision(2) << 95.5;
    std::string result = oss.str();
    std::cout << result << std::endl;
    
    // istringstream：解析字符串
    std::istringstream iss("123 45.67 hello");
    int num;
    double d;
    std::string str;
    iss >> num >> d >> str;
    std::cout << num << ", " << d << ", " << str << std::endl;
    
    // 格式化输出
    double pi = 3.14159265358979;
    std::cout << std::setw(15) << std::setprecision(4) << pi << std::endl;
    std::cout << std::setw(15) << std::left << pi << std::endl;
    std::cout << std::setw(15) << std::right << pi << std::endl;
    
    // 进制转换
    int value = 255;
    std::cout << "Decimal: " << std::dec << value << std::endl;
    std::cout << "Hex: " << std::hex << value << std::endl;
    std::cout << "Octal: " << std::oct << value << std::endl;
    
    return 0;
}

#include <iostream>
#include <fstream>

int main() {
    std::ifstream file("test.txt");
    
    // 检查IO状态
    if (file.good()) {
        std::cout << "Stream is in good state" << std::endl;
    }
    
    // 逐词读取
    std::string word;
    while (file >> word) {
        std::cout << word << " ";
    }
    
    // 检查为什么循环结束
    if (file.eof()) {
        std::cout << "\nReached end of file" << std::endl;
    }
    if (file.fail()) {
        std::cout << "A format error occurred" << std::endl;
    }
    if (file.bad()) {
        std::cout << "A serious I/O error occurred" << std::endl;
    }
    
    // 清除错误状态
    file.clear();
    
    file.close();
    return 0;
}

#include <iostream>
#include <fstream>
#include <string>

bool copyFile(const std::string &src, const std::string &dst) {
    std::ifstream infile(src, std::ios::binary);
    if (!infile) {
        std::cerr << "Cannot open source file: " << src << std::endl;
        return false;
    }
    
    std::ofstream outfile(dst, std::ios::binary);
    if (!outfile) {
        std::cerr << "Cannot open destination file: " << dst << std::endl;
        return false;
    }
    
    char buffer[4096];
    while (infile.read(buffer, sizeof(buffer))) {
        outfile.write(buffer, infile.gcount());
    }
    // 写入剩余数据
    outfile.write(buffer, infile.gcount());
    
    infile.close();
    outfile.close();
    return true;
}

int main(int argc, char *argv[]) {
    if (argc != 3) {
        std::cerr << "Usage: " << argv[0] << " source destination" << std::endl;
        return 1;
    }
    
    if (copyFile(argv[1], argv[2])) {
        std::cout << "File copied successfully" << std::endl;
    }
    
    return 0;
}

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

struct Record {
    std::string name;
    int age;
    std::string city;
};

std::vector<Record> readCSV(const std::string &filename) {
    std::vector<Record> records;
    std::ifstream file(filename);
    
    std::string line;
    std::getline(file, line);  // 跳过标题行
    
    while (std::getline(file, line)) {
        std::istringstream iss(line);
        Record r;
        std::string token;
        
        std::getline(iss, token, ',');
        r.name = token;
        
        std::getline(iss, token, ',');
        r.age = std::stoi(token);
        
        std::getline(iss, token, ',');
        r.city = token;
        
        records.push_back(r);
    }
    
    return records;
}

int main() {
    // 创建测试CSV
    std::ofstream csv("data.csv");
    csv << "name,age,city" << std::endl;
    csv << "Alice,20,Beijing" << std::endl;
    csv << "Bob,25,Shanghai" << std::endl;
    csv << "Charlie,30,Guangzhou" << std::endl;
    csv.close();
    
    auto records = readCSV("data.csv");
    for (const auto &r : records) {
        std::cout << r.name << ", " << r.age << ", " << r.city << std::endl;
    }
    
    return 0;
}