C++中string庫與自定義類型的轉(zhuǎn)換

在C++中，std::string庫提供了許多用于處理字符串的操作。如果你需要將自定義類型與std::string進(jìn)行轉(zhuǎn)換，你可以使用以下方法：

1. 使用std::to_string函數(shù)： std::to_string函數(shù)可以將數(shù)值類型（如整數(shù)、浮點(diǎn)數(shù)等）轉(zhuǎn)換為std::string。例如：

#include <iostream>
#include <string>

int main() {
    int num = 42;
    std::string str = std::to_string(num);
    std::cout << "The string representation of " << num << " is: " << str << std::endl;
    return 0;
}

對于自定義類型，你可以重載operator<<以支持直接輸出到std::ostream，然后使用std::ostringstream進(jìn)行轉(zhuǎn)換：

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

class MyType {
public:
    int value;

    MyType(int v) : value(v) {}

    friend std::ostream& operator<<(std::ostream& os, const MyType& obj) {
        os << obj.value;
        return os;
    }
};

int main() {
    MyType obj(42);
    std::string str = obj;  // 使用重載的operator<<
    std::cout << "The string representation of " << obj << " is: " << str << std::endl;
    return 0;
}

2. 使用std::stoi和std::stod函數(shù)： std::stoi和std::stod函數(shù)可以將std::string轉(zhuǎn)換為整數(shù)和浮點(diǎn)數(shù)。例如：

#include <iostream>
#include <string>
#include <stdexcept>

int main() {
    std::string str = "42";
    try {
        int num = std::stoi(str);
        std::cout << "The integer representation of " << str << " is: " << num << std::endl;
    } catch (const std::invalid_argument& e) {
        std::cerr << "Invalid argument: " << e.what() << std::endl;
    } catch (const std::out_of_range& e) {
        std::cerr << "Out of range: " << e.what() << std::endl;
    }

    str = "3.14";
    try {
        double d = std::stod(str);
        std::cout << "The double representation of " << str << " is: "<< d << std::endl;
    } catch (const std::invalid_argument& e) {
        std::cerr << "Invalid argument: " << e.what() << std::endl;
    } catch (const std::out_of_range& e) {
        std::cerr << "Out of range: " << e.what() << std::endl;
    }

    return 0;
}

對于自定義類型，你可以重載operator>>以支持從std::istream讀取，然后使用std::istringstream進(jìn)行轉(zhuǎn)換：

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

class MyType {
public:
    int value;

    MyType(int v) : value(v) {}

    friend std::istream& operator>>(std::istream& is, MyType& obj) {
        is >> obj.value;
        return is;
    }
};

int main() {
    std::string str = "42";
    std::istringstream iss(str);
    MyType obj;
    iss >> obj;  // 使用重載的operator>>
    std::cout << "The MyType value is: " << obj.value << std::endl;

    str = "3.14";
    iss.clear();
    iss.str(str);
    obj.value = 0;
    iss >> obj.value;  // 使用重載的operator>>
    std::cout << "The MyType value is: " << obj.value << std::endl;

    return 0;
}

這些方法可以幫助你在std::string和自定義類型之間進(jìn)行轉(zhuǎn)換。