C ++-排序算法看不到我的重载“<”用户定义类型的运算符。 [英] C++ - sort algorithm doesnt see my overloaded "<" operator for user-defined type.

问题描述

好，所以我有1个名为 fraction 的用户定义类型，它表示具有分子和分母的普通分数。以下是代码：

Ok so I have 1 user-defined type named fraction and it represents and ordinary fraction with a numerator and denominator. Here is the code:

class Fraction
{
private:
  int numerator;
  int denominator;

public:
  Fraction(int numer,int denom)
    :numerator(numer),denominator(denom){}

  int get_denom(){return denominator;}
  int get_numer(){return numerator;}
};

如您所见，它完全在头文件中实现。

As you see it is completly implemented in a header file.

所以我要用排序算法对分数向量进行排序。这是重载的<代码运算符（请注意：它与Fraction类放在同一文件中，但位于类之外）：

So what I want to do with this is sort a vector of fractions using the sort algorithm. Here is code of overloaded "<" operator (note: It is placed in same file as the Fraction class, but outside of the class):

bool operator<(Fraction& first,Fraction& second)
{
  if(first.get_denom() == second.get_denom())
  {
    return first.get_numer()<second.get_numer()?true:false;
  }
  int first_num=first.get_denom();
  int second_num=second.get_denom();
  int lcm=(first_num*second_num)/gcd(first_num,second_num);
  int first_new_numerator=(lcm/first_num)*first.get_numer();
  int second_new_numerator=(lcm/second_num)*second.get_numer();

  return first_new_numerator<second_new_numerator?true:false;
}

它的作用是检查分母是否相等，然后测试分子的值。如果它们不相等，则使用最小公倍数和gcd使它们相等。

What it does is check if denominators are equal if they are then it tests the values of numerators. If they are not equal it equalizes them using least common multiple and gcd.

真正的问题开始于当我想在main中使用排序算法时（编译时错误）。以下是主要代码：

The real problem starts when I want to use the sort algorithm in main (compile time error).Here is the main code:

Fraction parse_fraction(string& input)
{

  stringstream fraction_string(input);
  int numer;
  fraction_string>>numer;
  char seperator;
  fraction_string>>seperator;
  int denom;
  fraction_string>>denom;

  return Fraction(numer,denom);
}


int main()
{
  vector<Fraction> fractions;
  string input;
  while(cin>>input)
  {
    if(input=="|") break;
    fractions.push_back(parse_fraction(input));
  }

  sort(fractions.begin(),fractions.end);

  for(int i=0;i<fractions.size();i++)
  {
    cout<<fractions[i];
  }

  return 0;
}

我得到的错误是（注意：我已经适当地重载了<< 小数运算符，但不想在此处造成混乱）：

Errors I get are (Note:I have properly overloaded "<<" operator for fractions but dont want to make clutter here):

/usr/include/c++/4.6/bits/stl_algo.h||In function ‘_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, const _Tp&) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Fraction*, std::vector<Fraction> >, _Tp = Fraction]’:|

/usr/include/c++/4.6/bits/stl_algo.h:2253|70|instantiated from ‘_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Fraction*, std::vector<Fraction> >]’|

/usr/include/c++/4.6/bits/stl_algo.h:2284|54|instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Fraction*, std::vector<Fraction> >, _Size = long int]’|

/usr/include/c++/4.6/bits/stl_algo.h:5330|4|instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<Fraction*, std::vector<Fraction> >]’|

/home/vanio/Desktop/workspace/C++/Ordner/main.cpp:35|43|instantiated from here|

/usr/include/c++/4.6/bits/stl_algo.h|2212|error: no match for ‘operator<’ in ‘__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = Fraction*, _Container = std::vector<Fraction>, __gnu_cxx::__normal_iterator<_Iterator, _Container>::reference = Fraction&]() < __pivot’|

/usr/include/c++/4.6/bits/stl_algo.h|2212|note: candidates are:|

/usr/include/c++/4.6/bits/stl_pair.h|207|note: template<class _T1, class _T2> bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)|

/usr/include/c++/4.6/bits/stl_iterator.h|291|note: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)|

/usr/include/c++/4.6/bits/stl_iterator.h|341|note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)|

/usr/include/c++/4.6/bits/basic_string.h|2510|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>&)|

/usr/include/c++/4.6/bits/basic_string.h|2522|note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)|

/usr/include/c++/4.6/bits/basic_string.h|2534|note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)|

/usr/include/c++/4.6/bits/stl_vector.h|1290|note: template<class _Tp, class _Alloc> bool std::operator<(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)|

/home/vanio/Desktop/workspace/C++/Ordner/Fraction.h|39|note: bool operator<(Fraction&, Fraction&)|

/home/vanio/Desktop/workspace/C++/Ordner/Fraction.h|39|note:   no known conversion for argument 2 from ‘const Fraction’ to ‘Fraction&’|

/usr/include/c++/4.6/bits/stl_algo.h|2215|error: no match for ‘operator<’ in ‘__pivot < __last.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = Fraction*, _Container = std::vector<Fraction>, __gnu_cxx::__normal_iterator<_Iterator, _Container>::reference = Fraction&]()’|

/usr/include/c++/4.6/bits/stl_algo.h|2215|note: candidates are:|

/usr/include/c++/4.6/bits/stl_pair.h|207|note: template<class _T1, class _T2> bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)|

/usr/include/c++/4.6/bits/stl_iterator.h|291|note: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)|

/usr/include/c++/4.6/bits/stl_iterator.h|341|note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)|

/usr/include/c++/4.6/bits/basic_string.h|2510|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>&)|

/usr/include/c++/4.6/bits/basic_string.h|2522|note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)|

/usr/include/c++/4.6/bits/basic_string.h|2534|note: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&)|

/usr/include/c++/4.6/bits/stl_vector.h|1290|note: template<class _Tp, class _Alloc> bool std::operator<(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)|

/home/vanio/Desktop/workspace/C++/Ordner/Fraction.h|39|note: bool operator<(Fraction&, Fraction&)|

/home/vanio/Desktop/workspace/C++/Ordner/Fraction.h|39|note:   no known conversion for argument 1 from ‘const Fraction’ to ‘Fraction&’|
||=== Build finished: 22 errors, 0 warnings ===|

推荐答案

bool operator<(Fraction& first,Fraction& second)

问题是您的<$ c $超载c> operator< 只接受非常量参数，但是算法试图将 Fraction 的常量引用与容器中的元素进行比较

The problem is that your overload of operator< only accepts non-const arguments, but the algorithm is trying to compare a constant reference to a Fraction with the elements in your container.

由于 operator< 不会修改比较对象的内容，因此应通过const引用来获取它们：

Since operator< does not modify the contents of the compared objects, it should take them by const reference:

bool operator<(Fraction const & first,Fraction const & second)

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