如何从 map<pair<string, int>, pair<string, Array>> 中迭代和查找？答案

【问题标题】：How to iterate and find from map<pair<string, int>, pair<string, Array>>?如何从 map<pair<string, int>, pair<string, Array>> 中迭代和查找？
【发布时间】：2019-12-27 08:28:46
【问题描述】：

这是我的地图：

map<pair<string, int>, pair<string, Array> > matchMap;

这是函数：

void Schedule::studentSchedule() 
{
    string s, c;
    cout << "Enter the student and course name to create schedule" << endl;
    cin >> s >> c;

    list<string>::iterator studentLoc;
    map<pair<string, int>, pair<string, Array> >::iterator courseL;

    studentLoc = find(getStudentList().begin(), getStudentList().end(), s);
    courseL = find(getMatchMap().begin(), getMatchMap().end(), c);

    if (studentLoc != getStudentList().end() && courseL != getMatchMap().end())
    {}
}

我在此处找不到字符串，因为出现错误：

courseL = find(getMatchMap().begin(),getMatchMap().end(),c);

我怎样才能找到我想要的元素？这是错误：

In file included from C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/stl_algobase.h:71,
                 from C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/algorithm:61,
                 from C:\Users\Fatih\Desktop\clion\SchoolProject1\Schedule.cpp:4:
C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/predefined_ops.h: In instantiation of 'bool __gnu_cxx::__ops::_Iter_equals_val<_Value>::operator()(_Iterator) [with _Iterator = std::_Rb_tree_iterator<std::pair<const std::pair<std::__cxx11::basic_string<char>, int>, std::pair<std::__cxx11::basic_string<char>, std::array<int, 6> > > >; _Value = const std::__cxx11::basic_string<char>]':
C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/stl_algo.h:104:42:   required from '_InputIterator std::__find_if(_InputIterator, _InputIterator, _Predicate, std::input_iterator_tag) [with _InputIterator = std::_Rb_tree_iterator<std::pair<const std::pair<std::__cxx11::basic_string<char>, int>, std::pair<std::__cxx11::basic_string<char>, std::array<int, 6> > > >; _Predicate = __gnu_cxx::__ops::_Iter_equals_val<const std::__cxx11::basic_string<char> >]'
C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/stl_algo.h:161:23:   required from '_Iterator std::__find_if(_Iterator, _Iterator, _Predicate) [with _Iterator = std::_Rb_tree_iterator<std::pair<const std::pair<std::__cxx11::basic_string<char>, int>, std::pair<std::__cxx11::basic_string<char>, std::array<int, 6> > > >; _Predicate = __gnu_cxx::__ops::_Iter_equals_val<const std::__cxx11::basic_string<char> >]'
C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/stl_algo.h:3905:28:   required from '_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = std::_Rb_tree_iterator<std::pair<const std::pair<std::__cxx11::basic_string<char>, int>, std::pair<std::__cxx11::basic_string<char>, std::array<int, 6> > > >; _Tp = std::__cxx11::basic_string<char>]'
C:\Users\Fatih\Desktop\clion\SchoolProject1\Schedule.cpp:24:63:   required from here
C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/predefined_ops.h:241:17: error: no match for 'operator==' (operand types are 'std::pair<const std::pair<std::__cxx11::basic_string<char>, int>, std::pair<std::__cxx11::basic_string<char>, std::array<int, 6> > >' and 'const std::__cxx11::basic_string<char>')
  { return *__it == _M_value; }
           ~~~~~~^~~~~~~~~~~
In file included from C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/stl_algobase.h:67,
                 from C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/algorithm:61,
                 from C:\Users\Fatih\Desktop\clion\SchoolProject1\Schedule.cpp:4:
C:/PROGRA~1/MINGW-~1/X86_64~1.0-P/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/stl_iterator.h:860:5: note: candidate: 'template<class _IteratorL, class _IteratorR, class _Container> bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator<_IteratorL, _Container>&, const __gnu_cxx::__normal_iterator<_IteratorR, _Container>&)'
     operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,

【问题讨论】：

标签： c++ algorithm c++11 data-structures stdmap

【解决方案1】：

你试过用find吗？

courseL = matchMap.find(pair<string, int>{c, 1});

您的地图的键是pair<string, int> 类型，因此要使用 find 您需要提供一个有效的键。

【讨论】：

我试过这样，但我又得到一个错误。查找错误没有匹配的成员函数
void Course::addCourse() { string a; int b; int total; int courseAdd; cout<<"How many course you want to add?"<<endl; cin>>courseAdd; cout<<"Enter the name of course and number of hours.\nWARNING:For now just enter max 6 course hours"<<endl; for(int i=0;i<courseAdd;++i) { setCourseName(a); setHours(b); getCourseList().insert({a, b}); total += getHours(); shuffleVector(); getMatchMap().insert({make_pair(a,b),make_pair(getDay1()[i],dayHours)}); }

【解决方案2】：

总之，看到这个错误，

no match for 'operator=='
(operand types are 'std::pair<const std::pair<std::__cxx11::basic_string<char>, int>, 
std::pair<std::__cxx11::basic_string<char>, std::array<int, 6> > >'
and 'const std::__cxx11::basic_string<char>')

您的地图的键（即getMatchMap()）是std::pair<std::string, int>，而不仅仅是std::string，而且您只传递了std::string。

你需要

std::find(getMatchMap().begin(), getMatchMap().end(), std::make_pair(s, /*some integer*/));
//                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

或者更合适的是使用std::map::find 成员函数。

const auto iter = getMatchMap().find(std::make_pair(s, /*some integer*/));

【讨论】：

但是我只需要在地图上找到课程名称。不是整数。
据我了解，getMatchMap 函数导致的错误。我用 Dror Moyal 的答案更改了代码，它似乎有效。
当我执行此解决方案时，我在运行代码时无法在地图上找到这些对。地图中的整数是用户定义的整数，我们实际上并不知道里面有什么。有没有办法在不发送整数的情况下找到课程名称？
courseL = find_if(getMatchMap().begin(),getMatchMap().end(),(courseL->first).first == c);我像这样更改了代码，但我又遇到了错误。
错误：表达式不能用作函数 { return bool(_M_pred(*__it)); } ^~~~~~~~~~~~~~~~~~~~~~~