遍历映射时出错<std：：string， std：：string>

Error when iterating through a map<std::string, std::string>

本文关键字：string std gt lt 映射 出错 遍历      更新时间：2023-10-16

我尝试了几种遍历"entries"映射的方法，但所有方法都产生相同的冗长错误消息。

dylan@Aspire-one:~$ g++ -std=c++11 dictionary.cpp
In file included from /usr/include/c++/4.8/map:60:0,
                 from dictionary.h:6,
                 from dictionary.cpp:1:
/usr/include/c++/4.8/bits/stl_tree.h: In instantiation of ‘void 
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, 
_Alloc>::_M_insert_unique(_II, _II) [with _InputIterator = 
std::basic_string<char>; _Key = std::basic_string<char>; _Val = 
std::pair<const std::basic_string<char>, std::basic_string<char> >; 
_KeyOfValue = std::_Select1st<std::pair<const std::basic_string<char>, 
std::basic_string<char> > >; _Compare = std::less<std::basic_string<char> 
>; _Alloc = std::allocator<std::pair<const std::basic_string<char>, 
std::basic_string<char> > >]’:
/usr/include/c++/4.8/bits/stl_map.h:226:11:   required from 
‘std::map<_Key, _Tp, _Compare, _Alloc>::map(_InputIterator, 
_InputIterator) [with _InputIterator = std::basic_string<char>; _Key = 
std::basic_string<char>; _Tp = std::basic_string<char>; _Compare = 
std::less<std::basic_string<char> >; _Alloc = 
std::allocator<std::pair<const std::basic_string<char>, 
std::basic_string<char> > >]’
dictionary.h:11:66:   required from here
/usr/include/c++/4.8/bits/stl_tree.h:1721:28: error: no match for 
‘operator++’ (operand type is ‘std::basic_string<char>’)
for (; __first != __last; ++__first)
                        ^
/usr/include/c++/4.8/bits/stl_tree.h:1722:29: error: no match for 
‘operator*’ (operand type is ‘std::basic_string<char>’)
    _M_insert_unique_(end(), *__first);
                         ^
dylan@Aspire-one:~$

这是我最近的代码。

dictionary.cpp 

#include "dictionary.h"
//I have included <string> <map> <iterator> "from dictionary.h"
bool dictionary::search_term(const std::string& term){
    std::map<std::string, std::string>::iterator it;
    for (it = entries.begin(); it != entries.end(); ++it){
        if(it->first != term);
        else return true;
    }return false;
};

所以错误在"dictionary.h"?

dictionary.h 

#ifndef DICTIONARY_H
#define DICTIONARY_H
#include <iterator>
#include <string>
#include <map>
class dictionary{
    public:
        dictionary(const std::string& title, const std::string& definition = "")
            : entries(std::map<std::string, std::string>(title, definition)){;};
        bool write_entry(const std::string& term, const std::string& definition = "");
        bool define_term(const std::string& term, const std::string& definition);
        bool erase_entry(const std::string& term);
        bool search_term(const std::string& term);
    private:
        std::map<std::string, std::string> entries;
};
#endif//DICTIONARY_H

在构造函数中，为map使用大括号初始化:

    dictionary(const std::string& title, const std::string& definition = "")
        : entries{ {title, definition} } {;};

(EDIT:忘记一层花括号)

或在构造函数体

中设置元素
    dictionary(const std::string& title, const std::string& definition = "")
    {
      entries[title] = definition;
    }

问题在于class dictionary的构造函数的定义。std::map没有接受单个键值对的构造函数，因此使用单个键值对进行初始化的最简单方法是使用通用初始化器语法。您需要两对大括号，一对用于键值对的列表，另一对用于要定义的单对:

dictionary(const std::string& title, const std::string& definition = "")
    : entries(std::map<std::string, std::string>(title, definition)){;};
dictionary(const std::string& title, const std::string& definition = "")
    : entries{ {title, definition} } {}
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