sort的用法

std::sort

default (1)	template <class RandomAccessIterator> void sort (RandomAccessIterator first, RandomAccessIterator last);
custom (2)	template <class RandomAccessIterator, class Compare> void sort (RandomAccessIterator first, RandomAccessIterator last, Compare comp);

Sort elements in range

Sorts the elements in the range  [first,last) into ascending order.

The elements are compared using  operator< for the first version, and  comp for the second.

Equivalent elements are not guaranteed to keep their original relative order (see  stable_sort).

Parameters

first, last

Random-access iterators to the initial and final positions of the sequence to be sorted. The range used is  [first,last), which contains all the elements between  first and  last, including the element pointed by  first but not the element pointed by  last.
RandomAccessIterator shall point to a type for which  swap is properly defined and which is both  move-constructible and  move-assignable.

comp

Binary function that accepts two elements in the range as arguments, and returns a value convertible to  bool. The value returned indicates whether the element passed as first argument is considered to go before the second in the specific strict weak ordering it defines.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.

//注意第三个参数的解释(我用红色标记的)，大意就是如果comp返回的是true，则第一个元素就排在第二个元素前面