字符串与原始字符串字面量

#include <iostream>
#include <string>
#include <regex>

int main() {
    // ---- 场景 1: Windows 文件路径 ----
    std::string escaped_path = "C:\\Users\\张三\\Documents\\论文.docx";
    std::string raw_path = R"(C:\Users\张三\Documents\论文.docx)";

    std::cout << "===== 文件路径 =====" << std::endl;
    std::cout << "转义写法:   " << escaped_path << std::endl;
    std::cout << "原始字符串: " << raw_path << std::endl;

    // ---- 场景 2: 正则表达式 ----
    // 匹配 3 位数字-4 位数字（如 010-1234）
    std::string escaped_regex = "\\d{3}-\\d{4}";
    std::string raw_regex = R"(\d{3}-\d{4})";

    std::cout << "\n===== 正则表达式 =====" << std::endl;
    std::cout << "转义写法:   " << escaped_regex << std::endl;
    std::cout << "原始字符串: " << raw_regex << std::endl;

    std::regex pattern(raw_regex);
    std::string test1 = "电话: 010-5678";
    std::string test2 = "电话: 010-567";

    std::cout << "\"" << test1 << "\" → "
              << std::boolalpha << std::regex_search(test1, pattern) << std::endl;
    std::cout << "\"" << test2 << "\" → "
              << std::regex_search(test2, pattern) << std::endl;

    // ---- 场景 3: JSON / HTML 内嵌 ----
    std::string json = R"({
    "name": "张三",
    "age": 20,
    "courses": ["C++", "数据结构"]
})";

    std::cout << "\n===== 内嵌 JSON =====" << std::endl;
    std::cout << json << std::endl;

    // ---- 场景 4: 多行 SQL 查询 ----
    std::string sql = R"SQL(
SELECT id, name, score
FROM students
WHERE score >= 60
  AND enrollment_year = 2024
ORDER BY score DESC
)SQL";

    std::cout << "===== SQL 查询 =====" << std::endl;
    std::cout << sql << std::endl;

    // ---- 场景 5: 自定义定界符 ----
    // 内容本身包含 )" 时需要自定义定界符
    std::string tricky = R"END(这里的字符串包含)"这个序列，但不会提前终止)END";

    std::cout << "===== 自定义定界符 =====" << std::endl;
    std::cout << tricky << std::endl;

    return 0;
}

#include <iostream>
#include <string>
#include <cstring>

int main() {
    // ---- 常用操作 ----
    std::string s1 = "Hello";
    std::string s2 = "World";

    // 拼接
    std::string s3 = s1 + ", " + s2 + "!";
    std::cout << "拼接: " << s3 << std::endl;

    // 查找
    size_t pos = s3.find("World");
    if (pos != std::string::npos) {
        std::cout << "\"World\" 在位置 " << pos << std::endl;
    }

    // 子串
    std::string sub = s3.substr(7, 5);  // 从位置 7 取 5 个字符
    std::cout << "子串: " << sub << std::endl;

    // 替换
    std::string s4 = "C++ is hard";
    s4.replace(7, 4, "fun");
    std::cout << "替换: " << s4 << std::endl;

    // ---- C 风格字符串处理 ----
    char buf[50];
    // strcpy(buf, s3.c_str());  // 不安全：buf 可能不够大
    strncpy(buf, s3.c_str(), sizeof(buf) - 1);
    buf[sizeof(buf) - 1] = '\0';
    std::cout << "\nC 风格拷贝: " << buf << std::endl;

    // ---- 短字符串优化 (SSO) 观察 ----
    std::string short_str = "hi";
    std::string long_str = "this is a very long string that exceeds the SSO buffer";

    std::cout << "\n===== 字符串内存布局 =====" << std::endl;
    std::cout << "短字符串 '" << short_str << "':" << std::endl;
    std::cout << "  sizeof: " << sizeof(short_str) << " 字节" << std::endl;
    std::cout << "  data() == 栈? " << std::boolalpha
              << (short_str.data() == reinterpret_cast<const char*>(&short_str))
              << " (可能由实现决定)" << std::endl;

    std::cout << "长字符串: sizeof " << sizeof(long_str)
              << " 字节" << std::endl;
    // 长字符串的 data() 肯定不在栈上

    // ---- 字符类型 ----
    std::cout << "\n===== 字符类型 =====" << std::endl;
    const wchar_t* wide = L"宽字符";
    const char16_t* u16 = u"UTF-16 字符串";
    const char32_t* u32 = U"UTF-32 字符串";

    std::wcout << L"宽字符输出: " << wide << std::endl;
    std::cout << "char16_t 字符串长度: " << std::char_traits<char16_t>::length(u16) << std::endl;
    std::cout << "char32_t 字符串长度: " << std::char_traits<char32_t>::length(u32) << std::endl;

    return 0;
}