C++ 中的智能指针和映射

Question

我正在尝试使用智能指针执行此程序：

//File user.h
#include <list>
#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include <memory>
#include <map>

using namespace std;

class User {
    string name;
    int id;
public:
    User(const string& name, int id) : name(name), id(id) {}
    int getID() const {return id;}
    ~User(){}
};

//File main.c
#include "user.h"
using namespace std;
typedef std::shared_ptr<User> UserPtr;
typedef map<string, UserPtr> Dict;

int main()
{
    Dict dict;
    dict = new User("Adams", 666);
    auto it = dict.find("Adams");

    if (it == dict.end())
        cout << "not found!" << endl;

    else
        cout << "id3: " << it->second->getID() << endl;

    return 0;
}

我之前用原始指针 (*) 测试过它并且它有效。尽管如此，当使用智能指针时，我得到以下错误：

main.cpp: In function ‘int main()’:
main.cpp:15:10: error: no match for ‘operator=’ (operand types are ‘Dict {aka std::map<std::basic_string<char>, std::shared_ptr<User> >}’ and ‘User*’)
     dict = new User("Adams", 666);
          ^
main.cpp:15:10: note: candidates are:
In file included from /usr/include/c++/4.8/map:61:0,
                 from user.h:10,
                 from main.cpp:3:
/usr/include/c++/4.8/bits/stl_map.h:264:7: note: std::map<_Key, _Tp, _Compare, _Alloc>& std::map<_Key, _Tp, _Compare, _Alloc>::operator=(const std::map<_Key, _Tp, _Compare, _Alloc>&) [with _Key = std::basic_string<char>; _Tp = std::shared_ptr<User>; _Compare = std::less<std::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::basic_string<char>, std::shared_ptr<User> > >]
       operator=(const map& __x)
       ^
/usr/include/c++/4.8/bits/stl_map.h:264:7: note:   no known conversion for argument 1 from ‘User*’ to ‘const std::map<std::basic_string<char>, std::shared_ptr<User> >&’
/usr/include/c++/4.8/bits/stl_map.h:279:7: note: std::map<_Key, _Tp, _Compare, _Alloc>& std::map<_Key, _Tp, _Compare, _Alloc>::operator=(std::map<_Key, _Tp, _Compare, _Alloc>&&) [with _Key = std::basic_string<char>; _Tp = std::shared_ptr<User>; _Compare = std::less<std::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::basic_string<char>, std::shared_ptr<User> > >]
       operator=(map&& __x)
       ^
/usr/include/c++/4.8/bits/stl_map.h:279:7: note:   no known conversion for argument 1 from ‘User*’ to ‘std::map<std::basic_string<char>, std::shared_ptr<User> >&&’
/usr/include/c++/4.8/bits/stl_map.h:300:7: note: std::map<_Key, _Tp, _Compare, _Alloc>& std::map<_Key, _Tp, _Compare, _Alloc>::operator=(std::initializer_list<std::pair<const _Key, _Tp> >) [with _Key = std::basic_string<char>; _Tp = std::shared_ptr<User>; _Compare = std::less<std::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::basic_string<char>, std::shared_ptr<User> > >]
       operator=(initializer_list<value_type> __l)
       ^
/usr/include/c++/4.8/bits/stl_map.h:300:7: note:   no known conversion for argument 1 from ‘User*’ to ‘std::initializer_list<std::pair<const std::basic_string<char>, std::shared_ptr<User> > >’

智能指针是否声明错误？

Answer 1

Dict 是 std::map 并且您试图将指向用户的指针分配给它是错误的。

你需要的是

dict["Adams"] = std::make_shared<User>("Adams", 666);

C++ 中的智能指针和映射

Smart pointers and map in C++

c++

dictionary

smart-pointers