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stockListType.cpp:58：从这里实例化

/usr/include/c++/4.2.1/bits/stl_algo.h:91: error: passing ‘const stockType’ as ‘this’ argument of ‘bool stockType::operator<(const stockType&)’ discards qualifiers
/usr/include/c++/4.2.1/bits/stl_algo.h:92: error: passing ‘const stockType’ as ‘this’ argument of ‘bool stockType::operator<(const stockType&)’ discards qualifiers
/usr/include/c++/4.2.1/bits/stl_algo.h:94: error: passing ‘const stockType’ as ‘this’ argument of ‘bool stockType::operator<(const stockType&)’ discards qualifiers
/usr/include/c++/4.2.1/bits/stl_algo.h:98: error: passing ‘const stockType’ as ‘this’ argument of ‘bool stockType::operator<(const stockType&)’ discards qualifiers
/usr/include/c++/4.2.1/bits/stl_algo.h:100: error: passing ‘const stockType’ as ‘this’ argument of ‘bool stockType::operator<(const stockType&)’ discards qualifiers

以上是我得到的错误，希望有人向我解释它的含义。我通过在重载运算符前面放置一个常量来解决该错误。我的程序是一个股票市场应用程序，它读取一个包含字符串、5 个双精度数和一个 int 的文件。我们通过字符串符号和索引增益对程序进行排序。这本书指示我使用向量来存储每个数据。正如您在下面看到的，重载运算符比较每个符号并使用容器的 sort 成员函数对其进行排序。我的问题是为什么我必须在 > 和 < 的重载运算符前面放置一个常量。但不适用于 >=、<=、==、!= 重载运算符。

//function was declared in stockType.h and implemented in stockType.cpp
bool operator<(const stockType& stock)//symbol is a string 
{
  return (symbols < stock.symbols)
}


 //The function below was defined in stockListType.h and implemented in 
 //   stockListType.cpp where I instantiated the object of stockType as a vector.
   //vector<stockType> list; was defined in stockListType.h file

   void insert(const& stockType item)
   {
      list.push_back(item);
      }
  void stockListType::sortStockSymbols()
    {
     sort(list.begin(), list.end());
     }
4

1 回答 1

22

The error message tells you that you that you are casting of const from your object in operator< function. You should add const to all member functions that don't modify member.

bool operator<(const stockType& stock) const
//                                     ^^^^^
{
  return (symbols < stock.symbols)
}

The reason why compiler complains about operator< is because std::sort uses operator< to compare the elements.

Also you have another syntax error in insert function.

Update:

void insert(const& stockType item);

to:

void insert(const stockType& item);
//                         ^^
于 2013-09-29T03:20:52.640 回答