Question

我有std::deque<CustomType>，我正在尝试删除其位置我不知道的成员。因此，我首先找到它然后将其删除。

/* 
  Remove from - members, which is the private variable of std::deque<User> type
*/
void Group::remove_member(User u) {  
    if(this->is_member(u)) {
           std::deque<User>::iterator iter;
           iter = std::find(this->members.begin(), this->members.end(), u);
           if(iter != this->members.end()) {
                this->members.erase(iter);
           }
     }
}

然而，编译器（GCC）抛出的错误似乎缺少运算符重载。

In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/algorithm:62,
from Group.cpp:4:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_algo.h: In function ‘_RandomAccessIterator std::__find(_RandomAccessIterator, _RandomAccessIterator, const _Tp&, std::random_access_iterator_tag) [with _RandomAccessIterator = std::_Deque_iterator<User, User&, User*>, _Tp = User]’:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_algo.h:4224:   instantiated from ‘_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = std::_Deque_iterator<User, User&, User*>, _Tp = User]’
Group.cpp:36:   instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_algo.h:174: error: no match for ‘operator==’ in ‘__first.std::_Deque_iterator<_Tp, _Ref, _Ptr>::operator* [with _Tp = User, _Ref = User&, _Ptr = User*]() == __val’
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_algo.h:178: error: no match for ‘operator==’ in ‘__first.std::_Deque_iterator<_Tp, _Ref, _Ptr>::operator* [with _Tp = User, _Ref = User&, _Ptr = User*]() == __val’
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_algo.h:182: error: no match for ‘operator==’ in ‘__first.std::_Deque_iterator<_Tp, _Ref, _Ptr>::operator* [with _Tp = User, _Ref = User&, _Ptr = User*]() == __val’
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_algo.h:186: error: no match for ‘operator==’ in ‘__first.std::_Deque_iterator<_Tp, _Ref, _Ptr>::operator* [with _Tp = User, _Ref = User&, _Ptr = User*]() == __val’
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_algo.h:194: error: no match for ‘operator==’ in ‘__first.std::_Deque_iterator<_Tp, _Ref, _Ptr>::operator* [with _Tp = User, _Ref = User&, _Ptr = User*]() == __val’
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_algo.h:198: error: no match for ‘operator==’ in ‘__first.std::_Deque_iterator<_Tp, _Ref, _Ptr>::operator* [with _Tp = User, _Ref = User&, _Ptr = User*]() == __val’
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_algo.h:202: error: no match for ‘operator==’ in ‘__first.std::_Deque_iterator<_Tp, _Ref, _Ptr>::operator* [with _Tp = User, _Ref = User&, _Ptr = User*]() == __val’

Answer 1

请参阅my comment。

我觉得你还没有宣布bool User::operator==(const User&)

错误告诉您它试图在*iterator == ...的实现中执行std::find。但问题是，您没有为operator==重载User。尝试在User中声明成员函数，如下所示......

bool operator==(const User&);

现在，定义它以在User之间提供一些有意义的语义相等，否则std::find不知道如何比较它们。

作为旁注，为什么Group::remove_member不是const User&而不是User？

Answer 2

与@oldrinb提到的一样，您需要明确告诉如何测试两个User类的相等性。否则，find算法将无法找到您要查找的项目。这是通过覆盖==运算符来完成的。

#include <iostream>
#include <deque>
#include <algorithm>

using namespace std;

class MyCustomClass{
  public:
    MyCustomClass(int id) : id_(id) { }

   // Would produce the same error without this
   bool operator==(const MyCustomClass& b){
     return id_ == b.id_;
   }

   int id(){ return id_; }

  private:
    int id_;
};

int main(void){
  deque<MyCustomClass> q;
  q.push_back(MyCustomClass(1));
  q.push_back(MyCustomClass(2));
  q.push_back(MyCustomClass(3));
  deque<MyCustomClass>::iterator it = 
    find(q.begin(), q.end(), MyCustomClass(2));

  if ( it != q.end() ){
    printf("Found\n");
    q.erase(it);
  }else{
    printf("Not Found!\n");
  }

  for(it = q.begin(); it != q.end() ; it++)
    printf("%d ", it->id());

  printf("\n");

  return 0;
}

从双端队列中删除时出错

2 个答案: