如何从C ++的迭代器中调用类成员函数？

我无法使用map的迭代器调用show函数。 有没有办法使用迭代器来做到这一点？

#include <iostream>
#include <string>
#include <map>
using namespace std;
class A 
{ 
    int i;
    public: 
    A(int pi):i(pi)   {  cout<<"A()n"; }
    void show() const { cout<<i<<endl; }
    ~A()   {  cout<<"~A()n"; }
};
int main()
{
    map<char, A > mymap;
    A a(9) , b(8) , c(7);
    mymap['a'] =  a;
    mymap['b'] =  b;
    mymap['c'] =  c;
    map<char,A >::iterator it;
    for(it = mymap.begin(); it != mymap.end() ; it++)
        (*(it->second)).show();
    return 0;
}

在使用it->second.show() ，我得到下面的错误：

在/usr/include/c++/4.9/bits/stl_map.h:63:0包含的文件中，从/usr/include/c++/4.9/map:61开始，从3：/usr/include/c++/4.9/tuple ：在std :: pair <_T1，_T2> :: pair（std :: tuple <_Args1 ...>＆，std :: tuple <_Args2 ...>＆，std :: _ Index_tuple <_Indexes1 .. 。>，std :: _ Index_tuple <_Indexes2 ...>）[with _Args1 = {char &&}; long unsigned int ..._ Indexes1 = {0ul}; _Args2 = {}; long unsigned int ..._ Indexes2 = {}; _T1 = const char; _T2 = A]'：/usr/include/c++/4.9/tuple:1093:63：需要从std :: pair <_T1，_T2> :: pair（std :: piecewise_construct_t，std :: tuple <_Args1 .. 。>，std :: tuple <_Args2 ...>）[with _Args1 = {char &&}; _Args2 = {}; _T1 = const char; _T2 = A]'/usr/include/c++/4.9/ext/new_allocator.h:120:4：需要从'void __gnu_cxx :: new_allocator <_Tp> :: construct（_Up *，_Args && ...）[With _Up = std :: pair; _Args = {const std :: piecewise_construct_t＆，std :: tuple，std :: tuple <>}; _Tp = std :: _ Rb_tree_node>]'/usr/include/c++/4.9/bits/alloc_traits.h:253:4：需要来自'static std :: _ Require :: __ construct_helper <_Tp，_Args> :: type> std： ：allocator_traits <_Alloc> :: _ S_construct（_Alloc＆，_Tp *，_Args && ...）[with _Tp = std :: pair; _Args = {const std :: piecewise_construct_t＆，std :: tuple，std :: tuple <>}; _Alloc = std :: allocator>>; std :: _ Require :: __ construct_helper <_Tp，_Args> :: type> = void]'/usr/include/c++/4.9/bits/alloc_traits.h:399:57：'static decltype（_S_construct（__ a，__p ，（forward <_Args>）（std :: allocator_traits :: construct :: __ args）...））std :: allocator_traits <_Alloc> :: construct（_Alloc＆，_Tp *，_Args && ...）[with _Tp = std ：：对; _Args = {const std :: piecewise_construct_t＆，std :: tuple，std :: tuple <>}; _Alloc = std :: allocator>>; decltype（_S_construct（__ a，__p，（forward <_Args>）（std :: allocator_traits :: construct :: __ args）...））=]'/usr/include/c++/4.9/bits/stl_tree.h:423 ：42：需要从'std :: _ Rb_tree_node <_Val> * std :: _ Rb_tree <_Key，_Val，_KeyOfValue，_Compare，_Alloc> :: _ M_create_node（_Args && ...）[with _Args = {const std :: piecewise_construct_t＆，std :: tuple，std :: tuple <>}; _Key = char; _Val = std :: pair; _KeyOfValue = std :: _ Select1st>; _Compare = std :: less; _Alloc = std :: allocator>; std :: _ Rb_tree <_Key，_Val，_KeyOfValue，_Compare，_Alloc> :: _ Link_type = std :: _ Rb_tree_node> *]'/usr/include/c++/4.9/bits/stl_tree.h:1790:64：'std :: _ Rb_tree <_Key，_Val，_KeyOfValue，_Compare，_Alloc> ::迭代器std :: _ Rb_tree <_Key，_Val，_KeyOfValue，_Compare，_Alloc> :: _ M_emplace_hint_unique（std :: _ Rb_tree <_Key，_Val，_KeyOfValue，_Compare，_Alloc > :: const_iterator，_Args && ...）[with _Args = {const std :: piecewise_construct_t＆，std :: tuple，std :: tuple <>}; _Key = char; _Val = std :: pair; _KeyOfValue = std :: _ Select1st>; _Compare = std :: less; _Alloc = std :: allocator>; std :: _ Rb_tree <_Key，_Val，_KeyOfValue，_Compare，_Alloc> :: iterator = std :: _ Rb_tree_iterator>; std :: _ Rb_tree <_Key，_Val，_KeyOfValue，_Compare，_Alloc> :: const_iterator = std :: _ Rb_tree_const_iterator>]'/usr/include/c++/4.9/bits/stl_map.h:519:8：'std： ：map <_Key，_Tp，_Compare，_Alloc> :: mapped_type＆std :: map <_Key，_Tp，_Compare，_Alloc> ::运算符[]（std :: map <_Key，_Tp，_Compare，_Alloc> :: key_type &&） [用_Key = char; _Tp = A; _Compare = std :: less; _Alloc = std :: allocator>; std :: map <_Key，_Tp，_Compare，_Alloc> :: mapped_type = A; std :: map <_Key，_Tp，_Compare，_Alloc> :: key_type = char]'17:14：必需从这里/usr/include/c++/4.9/tuple:1104:70：错误：没有匹配函数调用'A :: A（）'second（std :: forward <_Args2>（std :: get <_Indexes2>（__ tuple2））...）^ /usr/include/c++/4.9/tuple:1104:70：note ：候选人是：9：5：注意：A :: A（int）9：5：注意：候选人期望1个参数，0提供5：7：注意：constexpr A :: A（常量A＆）5：7： ：候选人期望1个参数，0提供

---

这个怎么样？ 朋友。

#include <iostream>
#include <string>
#include <map>
using namespace std;
class A 
{ 
    int i;
public: 
    A(int pi=0):i(pi)   {  cout<<"A()n"; }
    void show() const { cout<<i<<endl; }
    ~A()   {  cout<<"~A()n"; }
};

int main()
{
    map<char, A > mymap;
    A a(9) , b(8) , c(7);
    mymap['a'] =  a;
    mymap['b'] =  b;
    mymap['c'] =  c;
    map<char,A >::iterator it;
    for(it = mymap.begin(); it != mymap.end() ; it++)
        it->second.show();
    return 0;
}

---

首先，您需要A中的默认构造函数：

A() {}

如果你已经提供了其他的c-tor，编译器不会创建默认的构造函数。

第二件事是如何调用你的函数：

it->second.show();

---

这将解决你的麻烦

    A(int pi=0):i(pi)   {  cout<<"A("<<pi<<")n"; }
...
    for(it = mymap.begin(); it != mymap.end() ; it++)
        (it->second).show();

你应该重载operator =以使其正常工作

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