find_end 源码剖析

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一：用法解析

函数原型：

equality (1)
template <class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
predicate (2)
template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);

功能：

在[ first1 , last1 )中搜索最后一个和区间[ first2 , last2 )匹配成功（默认是对应元素相等，重载是使pred为真）的区间，如果找到，返回[ first1 ,last1 )区间内最后匹配成功区间的首元素迭代器；否则返回last1。

例子：

// find_end example#include <iostream>     // std::cout#include <algorithm>    // std::find_end#include <vector>       // std::vectorbool myfunction (int i, int j) {  return (i==j);}int main () {  int myints[] = {1,2,3,4,5,1,2,3,4,5};  std::vector<int> haystack (myints,myints+10);  int needle1[] = {1,2,3};  // using default comparison:  std::vector<int>::iterator it;  it = std::find_end (haystack.begin(), haystack.end(), needle1, needle1+3);  if (it!=haystack.end())    std::cout << "needle1 last found at position " << (it-haystack.begin()) << '\n';  int needle2[] = {4,5,1};  // using predicate comparison:  it = std::find_end (haystack.begin(), haystack.end(), needle2, needle2+3, myfunction);  if (it!=haystack.end())    std::cout << "needle2 last found at position " << (it-haystack.begin()) << '\n';  return 0;}

运行如下：

needle1 found at position 5
needle2 found at position 3

二：源码剖析

// TEMPLATE FUNCTION find_end WITH PREDtemplate<class _FwdIt1,    class _FwdIt2,    class _Diff1,    class _Diff2,    class _Pr> inline    _FwdIt1 _Find_end(_FwdIt1 _First1, _FwdIt1 _Last1,        _FwdIt2 _First2, _FwdIt2 _Last2, _Pr _Pred, _Diff1 *, _Diff2 *)    {   // find last [_First2, _Last2) satisfying _Pred    _Diff1 _Count1 = 0;    _Distance(_First1, _Last1, _Count1);//区间长度    _Diff2 _Count2 = 0;    _Distance(_First2, _Last2, _Count2);    _FwdIt1 _Ans = _Last1;    if (0 < _Count2)        {   // validate _Pred and test        _DEBUG_POINTER_IF(_Count2 <= _Count1, _Pred);//判断区间长度是否合理,函数指针是否有效        for (; _Count2 <= _Count1; ++_First1, (void)--_Count1)            {   // room for match, try it            _FwdIt1 _Mid1 = _First1;            for (_FwdIt2 _Mid2 = _First2; ; ++_Mid1)                if (!_Pred(*_Mid1, *_Mid2))                    break;                else if (++_Mid2 == _Last2)                    {   // potential answer, save it                    _Ans = _First1;                    break;                    }            }        }    return (_Ans);    }template<class _FwdIt1,    class _FwdIt2,    class _Pr> inline    _FwdIt1 find_end(_FwdIt1 _First1, _FwdIt1 _Last1,        _FwdIt2 _First2, _FwdIt2 _Last2, _Pr _Pred)    {   // find last [_First2, _Last2) satisfying _Pred    _DEBUG_RANGE(_First1, _Last1);    _DEBUG_RANGE(_First2, _Last2);    return (_Rechecked(_First1,        _Find_end(_Unchecked(_First1), _Unchecked(_Last1),            _Unchecked(_First2), _Unchecked(_Last2), _Pred,            _Dist_type(_First1), _Dist_type(_First2))));    }        // TEMPLATE FUNCTION find_endtemplate<class _FwdIt1,    class _FwdIt2> inline    _FwdIt1 find_end(_FwdIt1 _First1, _FwdIt1 _Last1,        _FwdIt2 _First2, _FwdIt2 _Last2)    {   // find last [_First2, _Last2) match    return (_STD find_end(_First1, _Last1, _First2, _Last2,        equal_to<>()));    }

友情提醒，老套路，源码要从底端往上读。

源码摘抄自Visual Studio 2015安装目录algorithm文件中。

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