c++ - 如何使用友元运算符存储一串字符？

Question

我正在尝试创建一个使用 Caesar Cipher 的程序使用类继承，但友元运算符不允许我使用 getline。我试过查找重载 getline 的不同方法，但我不确定我做错了什么(我最近才停止使用命名空间 std，所以那里可能有几个错误)。

它仍在进行中。我不知道我是否需要长度，或者如果那些重载的 + 运算符实际上会向旧字符串添加额外的单词，例如(虽然我稍后可以弄清楚，我只是想知道我如何在这里正确使用 getline ).感谢您的帮助。

#include <iostream>
#include <string>


class Sentence{

    private:
        std::string codeSentence;
        int length;

    public:
        Sentence();
        Sentence(std::string codeSentence);
        Sentence(const Sentence &obj);
        ~Sentence();
        void setS (std::string codeSentence);
        std::string getS() const;
        Sentence & operator = (const Sentence &obj);
        Sentence operator +(const Sentence &obj) const;
        Sentence operator +(std::string codeSentence) const;
        friend Sentence operator +(std::string codeSentence, const Sentence &obj);
        friend std::ostream & operator << (std::ostream & out, const Sentence &obj);
        friend std::istream & operator >> (std::istream & in, Sentence &obj);
        friend std::istream & getline (std::istream & in, const Sentence & obj);
    };

Sentence::Sentence(){
}

Sentence::Sentence(const Sentence &obj){
    (*this) = obj;
}

Sentence::Sentence(std::string codeSentence){
    this->codeSentence = codeSentence;
}

Sentence::~Sentence(){
}

void Sentence::setS(std::string codeSentence){
    this->codeSentence = codeSentence;
}

std::string Sentence::getS() const{
    return (this-> codeSentence);
}

Sentence & Sentence::operator=(const Sentence &obj){
    this->codeSentence = obj.codeSentence;
    return (*this);
}

Sentence Sentence::operator+(const Sentence &obj) const{
    return (Sentence(this->codeSentence + ' ' + obj.codeSentence));
}

Sentence Sentence::operator+(std::string codeSentence) const{
    return (Sentence(this->codeSentence + ' ' + codeSentence));
}

Sentence operator+(std::string codeSentence, const Sentence &obj){
    return (Sentence(codeSentence + ' ' + obj.codeSentence));
}

std::istream & getline (std::istream & in, const Sentence & obj){
    if (in >> obj.length)
        getline(in, obj.codeSentence);
    return (in);
}

std::istream & operator >> (std::istream & in, Sentence &obj){

    in.getline(obj.codeSentence, sizeof(obj.codeSentence));
    return (in);
}

Answer 1

getLine 的问题在于您正在修改作为 const 传入的 Sentence。只需去掉const；毕竟你想修改它。