如何修复 C++ 中的“与 operator+ 不匹配”？

我正在编写一个重载一些基本运算符的类。我已经使用相同的概念和语法编写了其他类，它们工作正常，但现在我收到了一个关于我的 operator+ 函数的错误，专门针对这个类。当我的客户端程序中没有编写“+”运算符时，一切都可以正常编译，但是当我使用“+”运算符用前两个对象中的数据总和初始化对象的数据时，就会产生错误。

我在本网站上查看了运营商超载常见问题解答以及其他一些类似问题，但没有一个对我有帮助。即因为错误似乎不会出现在不同的计算机上。我将代码发送给我的教授，他被难住了，因为他无法重现我遇到的错误。

我的代码位于三个单独的文件中：mystring.h、mystring.cpp 和 simpleclient.cpp。我将包含每个文件中的相关代码，因为其余代码应该无关紧要，但是如果您希望我包含整个文件，我可以这样做。

我的字符串.h：

#include <iostream>
#include <cstring>
#ifndef MYSTRING_H
#define MYSTRING_H
namespace cs_mystring{
    class MyString {
        public:
            MyString(const char* = "");
            MyString(const MyString& right);
            ~MyString();
            MyString operator=(const MyString& right);
            friend MyString operator+(const MyString& left, const MyString& right);
            //OTHER FUNCTION DECLARATIONS
        private:
            char* data;
    };
}
#endif

我的字符串.cpp：

#include <iostream>
#include <cstring>
#include <cassert>
#include "mystring.h"

namespace cs_mystring{
    //DEFAULT CONSTRUCTOR
    MyString::MyString(const char* init){
        data = new char[strlen(init) + 1];
        strcpy(data, init);
    }
    //COPY CONSTRUCTOR
    MyString::MyString(const MyString& right){
        data = new char[strlen(right.data) + 1];
        strcpy(data, right.data);
    }
    //DESTRUCTOR
    MyString::~MyString(){
        delete[] data;
    }
    //TODO
    MyString operator+(const MyString& left, const MyString& right){
        MyString temp;

        const int bufferSize = sizeof(left.data) + sizeof(right.data) + 2;
        char buffer[bufferSize];
        strcpy(buffer, left.data);
        strcat(buffer, right.data);
        temp = MyString(buffer);

        return temp;
    }
    //ASSIGNMENT OPERATOR
    MyString MyString::operator=(const MyString& right){
        if(this != &right){
            delete[] data; //remove the value stored in the heap
            data = new char[strlen(right.data) + 1]; //allocate memory for the new value
            strcpy(data, right.data); //copy the right-hand value into the new memory
        }
        return *this; //return the left hand object with the new value in the pointed-to memory location
    }

    //OTHER FUNCTION IMPLEMENTATIONS

}

简单客户端.cpp：

#include "mystring.h"
#include <fstream>
#include <cctype>      // for toupper()
#include <string>     
#include <cassert>
#include <iostream>
using namespace std;
using namespace cs_mystring;

int main(){

    //Simplest way to produce the error
    MyString a = MyString("Hello, ");
    MyString b = MyString("World!");
    MyString c = a + b;//Error is produced here
}

这里的想法是 MyString c 的数据成员将包含“Hello, World!”。

我使用以下命令编译并执行程序：

$ cd ~/Directory/with/the/files
$ g++ mystring.h mystring.cpp simpleclient.cpp -o exec
$ ./exec

当客户端程序包含错误代码时，我在第二个命令后从终端收到以下输出：

$ g++ mystring.cpp simpleclient.cpp -o exec
simpleclient.cpp: In function ‘int main()’:
simpleclient.cpp:16:20: error: no match for ‘operator+’ (operand types are ‘cs_mystring::MyString’ and ‘cs_mystring::MyString’)
     MyString c = a + b;
                    ^
In file included from /usr/include/c++/5/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/5/bits/char_traits.h:39,
                 from /usr/include/c++/5/ios:40,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from mystring.h:1:
/usr/include/c++/5/bits/stl_iterator.h:334:5: note: candidate: template<class _Iterator> std::reverse_iterator<_Iterator> std::operator+(typename std::reverse_iterator<_Iterator>::difference_type, const std::reverse_iterator<_Iterator>&)
     operator+(typename reverse_iterator<_Iterator>::difference_type __n,
     ^
/usr/include/c++/5/bits/stl_iterator.h:334:5: note:   template argument deduction/substitution failed:
simpleclient.cpp:16:22: note:   ‘cs_mystring::MyString’ is not derived from ‘const std::reverse_iterator<_Iterator>’
     MyString c = a + b;
                      ^
In file included from /usr/include/c++/5/string:52:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from mystring.h:1:
/usr/include/c++/5/bits/basic_string.h:4783:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
     ^
/usr/include/c++/5/bits/basic_string.h:4783:5: note:   template argument deduction/substitution failed:
simpleclient.cpp:16:22: note:   ‘cs_mystring::MyString’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’
     MyString c = a + b;
                      ^
In file included from /usr/include/c++/5/string:53:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from mystring.h:1:
/usr/include/c++/5/bits/basic_string.tcc:1151:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(const _CharT*, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
     operator+(const _CharT* __lhs,
     ^
/usr/include/c++/5/bits/basic_string.tcc:1151:5: note:   template argument deduction/substitution failed:
simpleclient.cpp:16:22: note:   mismatched types ‘const _CharT*’ and ‘cs_mystring::MyString’
     MyString c = a + b;
                      ^
In file included from /usr/include/c++/5/string:53:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from mystring.h:1:
/usr/include/c++/5/bits/basic_string.tcc:1167:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(_CharT, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
     operator+(_CharT __lhs, const basic_string<_CharT, _Traits, _Alloc>& __rhs)
     ^
/usr/include/c++/5/bits/basic_string.tcc:1167:5: note:   template argument deduction/substitution failed:
simpleclient.cpp:16:22: note:   ‘cs_mystring::MyString’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’
     MyString c = a + b;
                      ^
In file included from /usr/include/c++/5/string:52:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from mystring.h:1:
/usr/include/c++/5/bits/basic_string.h:4820:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
     ^
/usr/include/c++/5/bits/basic_string.h:4820:5: note:   template argument deduction/substitution failed:
simpleclient.cpp:16:22: note:   ‘cs_mystring::MyString’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’
     MyString c = a + b;
                      ^
In file included from /usr/include/c++/5/string:52:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/ostream:38,
                 from /usr/include/c++/5/iostream:39,
                 from mystring.h:1:
/usr/include/c++/5/bits/basic_string.h:4836:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Alloc> std::operator+(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, _CharT)
     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, _CharT __rhs)
     ^
/usr/include/c++/5/bits/basic_string.h:4836:5: note:   template argument deduction/substitution failed:
simpleclient.cpp:16:22: note:   ‘cs_mystring::MyString’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’
     MyString c = a + b;
                      ^

如果你能解释这个错误和输出的含义以及如何修复它，那将解决我的问题。