c++ - 在 vector 上使用算法中的查找函数

Question

我想在 vector 对象上使用算法库中的查找函数。 vector对象是customers的 vector ，(Customer是我做的一个类)。我第一次运行它时，它在 STL_algo.h 中给了我一个错误。我在网上搜索它，我也在此处搜索它，我在这里发现了一个关于它的问题，我运行了相同的代码，但我仍然遇到该错误。

我的代码在这里:

头文件:

#include <string>
#include <sstream>
#include <map>
#include <vector>

using namespace std;

enum Status {ACTIVE, INACTIVE};

class Customer {
    private:
        // ID Database class for storing customers' ids
        class IdDB {
            private:
                friend class Customer;

                // member field
                static map <string, int> idList;

                // member function
                static int getNumber (const string &threeLetters) {
                    map<string, int>::iterator i = idList.find(threeLetters);

                    if (i == idList.end()) {
                        idList.insert(pair <string, int> (threeLetters, 0));
                        return 0;
                    }else{
                        return ++(i->second);
                    }
                }
        };

        string id;
        string name;
        string address;
        Status status;

        void makeId () {
            string threeLetters = name.substr(0, 3);
            int idNum = IdDB::getNumber(threeLetters);

            stringstream oss;
            oss << threeLetters << idNum;
            id = oss.str();
        }

    public:
        Customer (const string&, const string&, const Status);

        // Accessor Methods
        string &getId ();
        string &getName ();
        string &getAddress ();
        Status getStatus ();

        // Mutator Methods
        void setAddress (const string&);
        void setStatus (const Status);

        // Misc. Methods
        void printStatus ();

        // Equality Operator Overloading
        friend bool operator == (Customer&, Customer&);
};

class CustomerDB {
    private:
        static vector<Customer> customersList;

    public:
        static void addCustomer (const Customer&);
        static void deleteCustomer (Customer&);
};

源代码:

#include <iostream>
#include <string>
#include <algorithm>
#include "Customer.h"

using namespace std;

map<string, int> Customer::IdDB::idList;

Customer::Customer (const string &cName, const string &cAddress, const Status cStatus) : name(cName), address(cAddress), status(cStatus) {
    makeId();
}

// Accessor Methods
string &Customer::getId () { return id; }
string &Customer::getName () { return name; }
string &Customer::getAddress () { return address; }
Status Customer::getStatus () { return status; }

// Mutator Methods
void Customer::setAddress (const string &newAddress) { address = newAddress; }
void Customer::setStatus (const Status newStatus) { status = newStatus; }

// Misc. Methods
void Customer::printStatus () {
    if (status == ACTIVE)
        cout << "Active";
    else
        cout << "In-Active";
}

vector<Customer> CustomerDB::customersList;

void CustomerDB::addCustomer (const Customer &customer) {
    customersList.push_back(customer);
}

void CustomerDB::deleteCustomer (Customer &customer) {
    vector<Customer>::iterator i;
    i = find(customersList.begin(), customersList.end(), customer); // getting error in here
}

// Equality Operator Overloading
bool operator == (Customer &cust1, Customer &cust2) {
    return cust1.getId() == cust2.getId();
}

在使用 Code::Blocks 构建之后，我明白了，

在头文件 STL_algo.h 中:

    }

  /// This is an overload used by find() for the RAI case.
  template<typename _RandomAccessIterator, typename _Tp>
    _RandomAccessIterator
    __find(_RandomAccessIterator __first, _RandomAccessIterator __last,
       const _Tp& __val, random_access_iterator_tag)
    {
      typename iterator_traits<_RandomAccessIterator>::difference_type
    __trip_count = (__last - __first) >> 2;

      for (; __trip_count > 0; --__trip_count)
    {
      if (*__first == __val) // error in here exactly getting a red block
        return __first;
      ++__first;

      if (*__first == __val)
        return __first;
      ++__first;

      if (*__first == __val)
        return __first;

谢谢

编辑:这是构建日志

Compiling: C:\Users\KiKo-SaMa\Desktop\C++\DVD_App\Customer.cpp
In file included from c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/algorithm:63:0,
                 from C:\Users\KiKo-SaMa\Desktop\C++\DVD_App\Customer.cpp:5:
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h: In function '_RandomAccessIterator std::__find(_RandomAccessIterator, _RandomAccessIterator, const _Tp&, std::random_access_iterator_tag) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Customer*, std::vector<Customer> >, _Tp = Customer]':
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h:4403:45:   instantiated from '_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator<Customer*, std::vector<Customer> >, _Tp = Customer]'
C:\Users\KiKo-SaMa\Desktop\C++\DVD_App\Customer.cpp:42:66:   instantiated from here
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h:162:4: error: no match for 'operator==' in '__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = Customer*, _Container = std::vector<Customer>, __gnu_cxx::__normal_iterator<_Iterator, _Container>::reference = Customer&]() == __val'
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h:162:4: note: candidates are:
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/postypes.h:218:5: note: template<class _StateT> bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_pair.h:201:5: note: template<class _T1, class _T2> bool std::operator==(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_iterator.h:285:5: note: template<class _Iterator> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_iterator.h:335:5: note: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/allocator.h:122:5: note: template<class _T1, class _T2> bool std::operator==(const std::allocator<_T1>&, const std::allocator<_T2>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/allocator.h:127:5: note: template<class _Tp> bool std::operator==(const std::allocator<_Tp1>&, const std::allocator<_Tp1>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2427:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2434:5: note: template<class _CharT> typename __gnu_cxx::__enable_if<std::__is_char<_Tp>::__value, bool>::__type std::operator==(const std::basic_string<_CharT>&, const std::basic_string<_CharT>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2448:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2460:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/streambuf_iterator.h:194:5: note: template<class _CharT, class _Traits> bool std::operator==(const std::istreambuf_iterator<_CharT, _Traits>&, const std::istreambuf_iterator<_CharT, _Traits>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_tree.h:309:5: note: template<class _Val> bool std::operator==(const std::_Rb_tree_iterator<_Tp>&, const std::_Rb_tree_const_iterator<_Val>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_tree.h:846:5: note: template<class _Key, class _Val, class _KeyOfValue, class _Compare, class _Alloc> bool std::operator==(const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&, const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_map.h:877:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator==(const std::map<_Key, _Tp, _Compare, _Alloc>&, const std::map<_Key, _Tp, _Compare, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_multimap.h:795:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator==(const std::multimap<_Key, _Tp, _Compare, _Alloc>&, const std::multimap<_Key, _Tp, _Compare, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_vector.h:1273:5: note: template<class _Tp, class _Alloc> bool std::operator==(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)
C:\Users\KiKo-SaMa\Desktop\C++\DVD_App\Customer.cpp:46:6: note: bool operator==(Customer&, Customer&)
C:\Users\KiKo-SaMa\Desktop\C++\DVD_App\Customer.cpp:46:6: note:   no known conversion for argument 2 from 'const Customer' to 'Customer&'
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h:4403:45:   instantiated from '_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator<Customer*, std::vector<Customer> >, _Tp = Customer]'
C:\Users\KiKo-SaMa\Desktop\C++\DVD_App\Customer.cpp:42:66:   instantiated from here
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h:166:4: error: no match for 'operator==' in '__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = Customer*, _Container = std::vector<Customer>, __gnu_cxx::__normal_iterator<_Iterator, _Container>::reference = Customer&]() == __val'
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h:166:4: note: candidates are:
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/postypes.h:218:5: note: template<class _StateT> bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_pair.h:201:5: note: template<class _T1, class _T2> bool std::operator==(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_iterator.h:285:5: note: template<class _Iterator> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_iterator.h:335:5: note: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/allocator.h:122:5: note: template<class _T1, class _T2> bool std::operator==(const std::allocator<_T1>&, const std::allocator<_T2>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/allocator.h:127:5: note: template<class _Tp> bool std::operator==(const std::allocator<_Tp1>&, const std::allocator<_Tp1>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2427:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2434:5: note: template<class _CharT> typename __gnu_cxx::__enable_if<std::__is_char<_Tp>::__value, bool>::__type std::operator==(const std::basic_string<_CharT>&, const std::basic_string<_CharT>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2448:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2460:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/streambuf_iterator.h:194:5: note: template<class _CharT, class _Traits> bool std::operator==(const std::istreambuf_iterator<_CharT, _Traits>&, const std::istreambuf_iterator<_CharT, _Traits>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_tree.h:309:5: note: template<class _Val> bool std::operator==(const std::_Rb_tree_iterator<_Tp>&, const std::_Rb_tree_const_iterator<_Val>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_tree.h:846:5: note: template<class _Key, class _Val, class _KeyOfValue, class _Compare, class _Alloc> bool std::operator==(const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&, const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_map.h:877:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator==(const std::map<_Key, _Tp, _Compare, _Alloc>&, const std::map<_Key, _Tp, _Compare, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_multimap.h:795:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator==(const std::multimap<_Key, _Tp, _Compare, _Alloc>&, const std::multimap<_Key, _Tp, _Compare, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_vector.h:1273:5: note: template<class _Tp, class _Alloc> bool std::operator==(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)
C:\Users\KiKo-SaMa\Desktop\C++\DVD_App\Customer.cpp:46:6: note: bool operator==(Customer&, Customer&)
C:\Users\KiKo-SaMa\Desktop\C++\DVD_App\Customer.cpp:46:6: note:   no known conversion for argument 2 from 'const Customer' to 'Customer&'
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h:170:4: error: no match for 'operator==' in '__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = Customer*, _Container = std::vector<Customer>, __gnu_cxx::__normal_iterator<_Iterator, _Container>::reference = Customer&]() == __val'
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h:170:4: note: candidates are:
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/postypes.h:218:5: note: template<class _StateT> bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_pair.h:201:5: note: template<class _T1, class _T2> bool std::operator==(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_iterator.h:285:5: note: template<class _Iterator> bool std::operator==(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_iterator.h:335:5: note: template<class _IteratorL, class _IteratorR> bool std::operator==(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/allocator.h:122:5: note: template<class _T1, class _T2> bool std::operator==(const std::allocator<_T1>&, const std::allocator<_T2>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/allocator.h:127:5: note: template<class _Tp> bool std::operator==(const std::allocator<_Tp1>&, const std::allocator<_Tp1>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2427:5: note: template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2434:5: note: template<class _CharT> typename __gnu_cxx::__enable_if<std::__is_char<_Tp>::__value, bool>::__type std::operator==(const std::basic_string<_CharT>&, const std::basic_string<_CharT>&)
Process terminated with status 1 (0 minutes, 1 seconds)
50 errors, 0 warnings

Answer 1

你应该研究你的 const 正确性，问题是你的相等比较器通过非 const 引用接受参数，但是 find 的最后一个参数是由 const 接受的引用，这意味着编译器不能在那里使用它。

顺便说一句，一旦您在其中添加了const，您将被迫向数据添加const 访问器。此外，如果您的运营商仅使用公共(public)接口(interface)，则无需将其声明为好友