C++ IO流详解：标准IO、文件IO与字符串IO实战

#include <iostream>
#include <iomanip> // 用于操纵符如 setw, setprecision
int main() {
    int num;
    double pi = 3.1415926535;
    char ch;
    // 输入整数
    std::cout << "请输入一个整数: ";
    std::cin >> num;
    if (std::cin.fail()) {
        std::cerr << "输入错误！请输入有效的整数。" << std::endl;
        std::cin.clear(); // 清除错误状态
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // 忽略错误输入行
        return 1;
    }
    // 输出整数和格式化后的浮点数
    std::cout << "你输入的整数是: " << num << std::endl;
    std::cout << "Pi 的值: " << std::setprecision(4) << std::fixed << pi << std::endl;
    // 输入字符 (注意 >> 会跳过空格)
    std::cout << "请输入一个字符: ";
    std::cin >> ch; // 如果缓冲区有残留的换行符，这里可能不会等待输入
    std::cout << "你输入的字符是: " << ch << std::endl;
    // 读取一行 (包括空格)
    std::cout << "请输入一行文本: ";
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // 清除之前的输入缓冲区
    std::string line;
    std::getline(std::cin, line); // 使用 getline 读取整行
    std::cout << "你输入的文本是: " << line << std::endl;
    return 0;
}

#include <iostream>
#include <fstream>
#include <string>
int main() {
    // 写入文件 (覆盖模式)
    std::ofstream outfile("data.txt"); // 默认模式: ios::out | ios::trunc
    if (!outfile.is_open()) {
        std::cerr << "打开文件 data.txt 用于写入失败！" << std::endl;
        return 1;
    }
    outfile << "Hello, File IO!" << std::endl;
    outfile << "This is a test line." << std::endl;
    outfile << "Writing numbers: " << 42 << std::endl;
    outfile.close(); // 关闭文件
    // 读取文件
    std::ifstream infile("data.txt");
    if (!infile.is_open()) {
        std::cerr << "打开文件 data.txt 用于读取失败！" << std::endl;
        return 1;
    }
    std::string line;
    std::cout << "文件内容:" << std::endl;
    while (std::getline(infile, line)) {
        std::cout << line << std::endl;
    }
    infile.close();
    // 追加模式写入
    std::ofstream appfile("data.txt", std::ios::app); // 追加模式
    if (appfile.is_open()) {
        appfile << "This line is appended." << std::endl;
        appfile.close();
    }
    return 0;
}

#include <iostream>
#include <fstream>
struct Person {
    char name[50];
    int age;
    double height;
};
int main() {
    Person p = {"Alice", 30, 1.75};
    // 写二进制文件
    std::ofstream b_outfile("person.dat", std::ios::binary);
    if (b_outfile.is_open()) {
        b_outfile.write(reinterpret_cast<char*>(&p), sizeof(Person));
        b_outfile.close();
    }
    // 读二进制文件
    Person p_read;
    std::ifstream b_infile("person.dat", std::ios::binary);
    if (b_infile.is_open()) {
        b_infile.read(reinterpret_cast<char*>(&p_read), sizeof(Person));
        b_infile.close();
        std::cout << "Name: " << p_read.name << std::endl;
        std::cout << "Age: " << p_read.age << std::endl;
        std::cout << "Height: " << p_read.height << std::endl;
    }
    return 0;
}

#include <iostream>
#include <sstream>
#include <string>
int main() {
    std::string data = "John Doe 30 1.85";
    std::istringstream iss(data);
    std::string firstname, lastname;
    int age;
    double height;
    iss >> firstname >> lastname >> age >> height;
    std::cout << "First Name: " << firstname << std::endl;
    std::cout << "Last Name: " << lastname << std::endl;
    std::cout << "Age: " << age << std::endl;
    std::cout << "Height: " << height << std::endl;
    return 0;
}

#include <iostream>
#include <sstream>
#include <string>
int main() {
    std::ostringstream oss;
    int num = 123;
    double value = 45.67;
    std::string text = "Formatted";
    oss << text << " output: Number=" << num << ", Value=" << value;
    std::string result = oss.str(); // 获取格式化后的字符串
    std::cout << result << std::endl; // 输出: Formatted output: Number=123, Value=45.67
    return 0;
}

#include <iostream>
#include <sstream>
#include <string>
int main() {
    std::stringstream ss;
    // 写入到字符串流
    ss << "Initial content. ";
    ss << 100 << " ";
    ss << 3.14;
    // 从字符串流读取
    std::string part;
    int num;
    double pi;
    ss >> part; // 读取到空格
    std::cout << "Part1: " << part << std::endl; // 输出: Initial
    ss >> part; // 继续读取下一个单词
    std::cout << "Part2: " << part << std::endl; // 输出: content.
    ss >> num;
    std::cout << "Number: " << num << std::endl; // 输出: 100
    ss >> pi;
    std::cout << "Pi: " << pi << std::endl; // 输出: 3.14
    return 0;
}