C++字符串处理全攻略

C++ string类详解

C++标准库中的string类是一个功能强大的字符串处理工具，它封装了字符序列的操作，提供了丰富的成员函数和操作符重载，极大简化了字符串处理任务。

string类的基本特性

string类位于<string>头文件中，属于std命名空间。它是一个模板类basic_string的特化版本，默认使用char类型作为字符类型。string对象动态管理内存，自动调整存储空间大小，无需手动管理内存分配和释放。

string类支持多种构造方式：

std::string s1;              // 空字符串
std::string s2("Hello");     // 从C风格字符串构造
std::string s3(5, 'A');      // 包含5个'A'字符
std::string s4(s2);          // 拷贝构造

string的常用操作

string类提供了丰富的成员函数用于字符串操作：

s.empty();      // 判断是否为空
s.size();       // 获取长度
s.length();     // 获取长度(同size)
s.c_str();      // 返回C风格字符串
s.substr(pos, n); // 获取子串
s.find(str);    // 查找子串

字符串可以通过+运算符连接，通过=赋值，通过==等比较运算符进行比较。string还支持类似数组的[]操作符访问单个字符。

string的内存管理

string对象会自动管理内存，但了解其内存策略有助于优化性能：

s.capacity();   // 返回当前分配的存储空间
s.reserve(n);   // 预分配内存
s.shrink_to_fit(); // 请求减少容量以适应大小

string与数值转换

C++11引入了方便的数值转换函数：

std::to_string(123);     // 数值转字符串
std::stoi("456");        // 字符串转int
std::stod("3.14");       // 字符串转double

string的高级特性

现代C++为string类添加了更多功能：

• 移动语义支持
• 字符串视图(string_view)兼容
• 用户定义字面量：using namespace std::string_literals; auto s = "Hello"s;

性能考虑

虽然string使用方便，但在性能关键场景需注意：

• 频繁的字符串连接应考虑使用ostringstream或预先分配足够空间
• 大量短字符串可考虑使用string_view避免拷贝
• 多线程环境下需注意线程安全问题

string类是C++中字符串处理的首选工具，合理使用可以编写出既安全又高效的字符串处理代码。

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