如何从具有用户定义数据类型的列表中删除元素? [英] How to remove an element from list having user defined data type?

问题描述

大家好，
我试图从为用户定义的数据类型创建的C ++列表中删除一个元素.由于模板未知用户定义类型上的==运算符，因此会引发错误.我该如何克服这个问题?

Hi all,
I am trying to remove an element from C++ list created for user defined data type. It is throwing error since == operator on a user defined type is unknown to template. How do I overcome this problem?

#include <iostream>
#include <list>

using namespace std;

 struct mem_list
    {
        unsigned int addr;
        int size;
    };


int main()
{

    list<mem_list> Mem_numbers;
    mem_list mem;
    mem_list *ptr_mem;
    mem.addr = 0xFF;
    mem.size = 10;

    Mem_numbers.push_front(mem);

    mem.addr = 0xAA;
    mem.size = 20;

    Mem_numbers.push_front(mem);


    mem.addr = 0xBB;
    mem.size = 30;

    Mem_numbers.push_front(mem);


    mem.addr = 0xCC;
    mem.size = 40;

    Mem_numbers.push_front(mem);


    mem.addr = 0xDD;
    mem.size = 50;

    Mem_numbers.push_front(mem);

    int counter = 0;

    for(list<mem_list>::const_iterator it = Mem_numbers.begin(); it != Mem_numbers.end(); ++it)
    {
        mem = *it;
        cout << mem.size<< " ";
    }

    cout << endl;

    for(list<mem_list>::const_iterator it = Mem_numbers.begin(); it != Mem_numbers.end(); ++it)
    {

            mem = *it;

            if( mem.size == 30)
            {
                Mem_numbers.remove(mem);
            }
    }


    for(list<mem_list>::const_iterator it = Mem_numbers.begin(); it != Mem_numbers.end(); ++it)
    {

            mem = *it;
            cout << mem.size<< " ";

    }

    cout << endl;

    return 0;
}

推荐答案

函数

std::list<t>::remove(const T&)</t>

在列表中搜索等于要传递的值的元素.为了测试相等性，它调用运算符

searches the list for an element that is equal to the value being passed. To test equality, it invokes the operator

bool operator==(const T& v1, const T& v2)

或替代地，运算符

bool T::operator==(const T& v) const

对于诸如int之类的内置类型，隐式定义了第一类运算符.但是对于用户定义的类型则不是.因此，您必须自己定义此运算符的两种形式之一:

For built-in types such as int, the first type of operator is implicitely defined. For user-defined types however it is not. Therefore you must define one of the two forms of this operator yourself:

bool operator==(const mem_list& v1, const mem_list& v2) {
   return v1.addr==v2.addr && v1.size==v2.size;
}
// or:
struct mem_list {
   unsigned int addr;
   int size;
   bool operator==(const struct mem_size& v) const {
      return v.size==size && v.addr==addr;
   }
};(

std::list元素必须必须具有等价性.将operator == ()添加到您的struct mem_list中，例如:

Hi,
std::list elements must be equality comparable. Add an operator == () to your struct mem_list like:

struct mem_list
{
    bool operator == (const mem_list& other)
    {
        return (addr == other.addr) && (size == other.size);
    }
    unsigned int addr;
    int size;
};

欢呼声，
AR
编辑(希望)正确答案

cheers,
AR
Edited for (hopefully) correct answer

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