[英]Error when iterating through a map<std::string, std::string>
I have tried several ways of iterating over my "entries" map, but all of them produce the same lengthy error message. 我尝试了几种遍历“入口”映射的方法,但是所有这些方法都会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:~$
Here is my most recent code. 这是我最近的代码。
dictionary.cpp 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;
};
So the error is in "dictionary.h"? 那么错误在“ dictionary.h”中吗?
dictionary.h 词典
#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
In the constructor, use brace initialization for the map: 在构造函数中,对地图使用花括号初始化:
dictionary(const std::string& title, const std::string& definition = "")
: entries{ {title, definition} } {;};
( EDIT: forgot one level of braces) ( 编辑:忘记一级括号)
or set the element in the constructor body 或在构造函数主体中设置元素
dictionary(const std::string& title, const std::string& definition = "")
{
entries[title] = definition;
}
The problem is in the definition of the constructor of class dictionary
. 问题在于
class dictionary
的构造函数的定义。 std::map
doesn't have a constructor that takes a single key-value pair, so the easiest way to initialize with one pair is to use the universal initializer syntax. std::map
没有采用单个键值对的构造函数,因此,使用一对初始化的最简单方法是使用通用的初始化语法。 You'll need two pairs of braces, one for the list of key-value pairs, and one for the single pair you want to define: 您将需要两对花括号,一对用于键-值对列表 ,一对用于您要定义的单对 :
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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