string类的用法

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char cstr[] = "Hello, World!";

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#include <string>
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std::string str = "Hello, World!";

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#include <iostream>
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#include <string>
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int main() {
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    std::string greeting = "Hello, C++ Strings!";
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    std::cout << greeting << std::endl;
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    return 0;
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}

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#include <iostream>
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#include <string>
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int main() {
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    std::string input;
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    std::cout << "请输入一个字符串：";
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    std::cin >> input; // 读取直到第一个空白字符
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    std::cout << "您输入的字符串是：" << input << std::endl;
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    return 0;
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}

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#include <iostream>
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#include <string>
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int main() {
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    std::string line;
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    std::cout << "请输入一行文本：";
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    std::getline(std::cin, line);
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    std::cout << "您输入的文本是：" << line << std::endl;
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    return 0;
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}

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#include <iostream>
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#include <string>
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int main() {
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    std::string first = "Hello, ";
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    std::string second = "World!";
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    std::string combined = first + second;
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    std::cout << combined << std::endl; // 输出: Hello, World!
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    return 0;
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}

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#include <iostream>
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#include <string>
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int main() {
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    std::string str = "Hello";
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    str.append(", World!");
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    std::cout << str << std::endl; // 输出: Hello, World!
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    return 0;
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}

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#include <iostream>
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#include <string>
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int main() {
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    std::string str = "Data";
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    str += " Structures";
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    std::cout << str << std::endl; // 输出: Data Structures
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    return 0;
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}

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a 和 b 不相等
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a 在字典序中小于 b

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#include <iostream>
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#include <string>
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int main() {
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    std::string str = "Hello, World!";
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    std::string sub = str.substr(7, 5); // 从位置7开始，长度5
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    std::cout << sub << std::endl; // 输出: World
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    return 0;
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}
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注意： 如果省略第二个参数，substr() 会返回从起始位置到字符串末尾的所有字符。
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std::string sub = str.substr(7); // 从位置7开始直到结束
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std::cout << sub << std::endl; // 输出: World!

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std::string sub = str.substr(7); // 从位置7开始直到结束
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std::cout << sub << std::endl; // 输出: World!

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#include <iostream>
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#include <string>
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int main() {
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    std::string str = "C++ Programming";
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    std::cout << "字符串长度: " << str.length() << std::endl; // 输出: 14
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    // 或者使用 size()
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    std::cout << "字符串大小: " << str.size() << std::endl; // 输出: 14
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    return 0;
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}

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#include <iostream>
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#include <string>
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int main() {
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    std::string str = "Hello";
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    std::cout << "初始容量: " << str.capacity() << std::endl;
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    str += ", World!";
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    std::cout << "追加后的容量: " << str.capacity() << std::endl;
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    return 0;
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}

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初始容量: 15
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追加后的容量: 15

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#include <iostream>
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#include <string>
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int main() {
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    std::string str = "ABCDE";
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    try {
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        char c = str.at(10); // 超出范围，会抛出异常
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    } catch (const std::out_of_range& e) {
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        std::cout << "异常捕获: " << e.what() << std::endl;
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    }
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    return 0;
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}

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异常捕获: basic_string::at: __n (which is 10) >= this->size() (which is 5)

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#include <iostream>
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#include <string>
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#include <algorithm>
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#include <cctype>
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int main() {
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    std::string str = "Hello, World!";
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    std::transform(str.begin(), str.end(), str.begin(),
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                   [](unsigned char c) { return std::toupper(c); });
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    std::cout << str << std::endl; // 输出: HELLO, WORLD!
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    return 0;
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}

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#include <iostream>
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#include <string>
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#include <algorithm>
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#include <cctype>
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int main() {
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    std::string str = "Hello, World!";
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    std::transform(str.begin(), str.end(), str.begin(),
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                   [](unsigned char c) { return std::tolower(c); });
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    std::cout << str << std::endl; // 输出: hello, world!
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    return 0;
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}

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std::string str;
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if (str.empty()) {
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    std::cout << "字符串为空。" << std::endl;
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}

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std::string str = "Clear me!";
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str.clear();
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std::cout << "str: " << str << std::endl; // 输出为空

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std::string str = "Hello, World!";
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str.erase(5, 7); // 从位置5开始，删除7个字符
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std::cout << str << std::endl; // 输出: Hello!

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std::string str = "Hello World";
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str.insert(5, ",");
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std::cout << str << std::endl; // 输出: Hello, World

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std::string str = "apple, banana, cherry";
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size_t pos = str.find_first_of(", ");
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std::cout << "第一个逗号或空格的位置: " << pos << std::endl; // 输出: 5

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#include <iostream>
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#include <sstream>
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#include <string>
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int main() {
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    std::stringstream ss;
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    ss << "Value: " << 42 << ", " << 3.14;
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    std::string result = ss.str();
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    std::cout << result << std::endl; // 输出: Value: 42, 3.14
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    return 0;
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}

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#include <iostream>
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#include <string>
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int main() {
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    int num = 100;
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    double pi = 3.14159;
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    std::string str1 = std::to_string(num);
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    std::string str2 = std::to_string(pi);
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    std::cout << "str1: " << str1 << ", str2: " << str2 << std::endl;
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    // 输出: str1: 100, str2: 3.141590
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    return 0;
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}

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#include <iostream>
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#include <string>
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int main() {
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    std::string numStr = "256";
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    std::string piStr = "3.14";
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    int num = std::stoi(numStr);
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    double pi = std::stod(piStr);
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    std::cout << "num: " << num << ", pi: " << pi << std::endl;
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    // 输出: num: 256, pi: 3.14
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    return 0;
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}

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5个字母的单词有:
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quick
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brown
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jumps
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leazy

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#include <iostream>
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#include <string>
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int main() {
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    std::string str = "Hello, std::string!";
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    const char* cstr = str.c_str();
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    std::cout << cstr << std::endl; // 输出: Hello, std::string!
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    return 0;
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}