compare

参考：C++ 中自定义比较器的正确姿势

function:

sort
- 1,2,3,4,5
- cmp使用方法：比较方法 or 比较器对象：std::greater<int>()
- ```
sort (myvector.begin()+4, myvector.end(), std::greater<int>());
```

class:

priority_queue
- 1,2,3,4,[5] (大顶堆)
- cmp使用方法：比较器类：std::greater<int>
- ```
priority_queue<int, std::vector<int>, std::greater<int> > third (myints,myints+4);
```
set
- 1,2,3,4,5
- cmp使用方法：比较器类：同上priority_queue
map
- key: 1,2,3,4,5
- cmp使用方法：比较器类：同上priority_queue

比较器类：struct:

greater
- >
- 5,4,3,2,1
less(default)
- <
- 1,2,3,4,5

参考：

greater：

1 template <class T> struct greater {
2   bool operator() (const T& x, const T& y) const {return x>y;}
3   typedef T first_argument_type;
4   typedef T second_argument_type;
5   typedef bool result_type;
6 };

less：

1 template <class T> struct less {
2   bool operator() (const T& x, const T& y) const {return x<y;}
3   typedef T first_argument_type;
4   typedef T second_argument_type;
5   typedef bool result_type;
6 };

自定义cmp类：

// CLASS For: map, multimap
struct classcomp_char {
  bool operator() (const char& lhs, const char& rhs) const
  {return lhs<rhs;}
};

// CLASS For: Type<int> : set, multiset, priority_queue
// OBJ For Function: sort
struct classcomp {
  bool operator() (const int& lhs, const int& rhs) const
  {return lhs<rhs;}
} myobject;

// Func For Function: sort
bool myfunction (int i,int j) { return (i<j); }


int main ()
{
  std::set<int,classcomp> set_test;                         // set
  std::multiset<int,classcomp> multiset_test;               // multiset
  std::map<char,int,classcomp_char> map_test;               // map
  std::multimap<char,int,classcomp_char> multimap_test;     // multimap

  // using mycomparison:
  typedef std::priority_queue<int,std::vector<int>,classcomp> mypq_type;
  mypq_type pq_test;                                        // priority_queue



  // using function as comp
  std::sort (myvector.begin()+4, myvector.end(), myfunction); // sort
  // using object as comp
    // 1.myobject
  std::sort (myvector.begin(), myvector.end(), myobject);     //sort
    // 2.classcomp()
  std::sort (myvector.begin(), myvector.end(), classcomp()); //sort

 return 0;
}