STL algorithm算法find_end(17)

原文地址：http://www.cplusplus.com/reference/algorithm/find_end/

function template

<algorithm>

std::find_end

equality (1)predicate (2)

template <class ForwardIterator1, class ForwardIterator2>
   ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1,
                              ForwardIterator2 first2, ForwardIterator2 last2);

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

Find last subsequence in range

Searches the range[first1,last1)for the last occurrence of the sequence defined by[first2,last2), and returns an iterator to its first element, orlast1if no occurrences are found.

查找在[first1,last1)中，与[first2,last2)范围内的元素最后一次匹配时出现的位置，并返回一个指向[frist1,last1)中匹配的第一个元素的迭代器，如果没有，则返回last1.

例子：

#include <iostream>
#include <vector>
#include <array>
#include <algorithm>
using namespace std;
void findend()
{
    vector<int> v1{1,2,3,4,5,6,3,4,9,8};
    int arr[]={9,8};
    array<double,2> ai{3,4};

    cout<<"v1=";
    for(int &i:v1)
        cout<<i<<"  ";
    cout<<endl;

    cout<<"arr=";
    for(int &i:arr)
        cout<<i<<"  ";

    cout<<endl<<"ai=";
    for(double &i:ai)
        cout<<i<<"  ";

    cout<<endl<<"auto it=find_end(v1.begin(),v1.end(),arr,arr+2);"<<endl;
    auto it=find_end(v1.begin(),v1.end(),arr,arr+2);
    cout<<"*(it-1)="<<*(it-1)<<endl;
    cout<<"*it="<<*it<<endl;
    cout<<"*(it+1)="<<*(it+1)<<endl;


    cout<<endl<<"auto it2=find_end(v1.begin(),v1.end(),ai.begin(),ai.end());"<<endl;
    auto it2=find_end(v1.begin(),v1.end(),ai.begin(),ai.end());
    cout<<"*(it2-1)="<<*(it2-1)<<endl;
    cout<<"*it2="<<*it2<<endl;
    cout<<"*(it2+1)="<<*(it2+1)<<endl;

}

运行截图：

The elements in both ranges are compared sequentially usingoperator==(orpred, in version(2)): A subsequence of[first1,last1)is considered a match only when this istrueforallthe elements of[first2,last2).

使用operator==进行比较，只有在[first1,last1)范围中中匹配的元素满足[first2,last2)都相等时，才算是匹配了。

This function returns the last of such occurrences. For an algorithm that returns the first instead, seesearch.

函数返回匹配出现的最后一次的位置。要返回第一次出现的位置，使用search.

The behavior of this function template is equivalent to:

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template<class ForwardIterator1, class ForwardIterator2> ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2) { if (first2==last2) return last1; // specified in C++11 ForwardIterator1 ret = last1; while (first1!=last1) { ForwardIterator1 it1 = first1; ForwardIterator2 it2 = first2; while (*it1==*it2) { // or: while (pred(*it1,*it2)) for version (2) ++it1; ++it2; if (it2==last2) { ret=first1; break; } if (it1==last1) return ret; } ++first1; } return ret; }

Parameters

first1, last1

Forward iteratorsto the initial and final positions of the searched sequence. The range used is[first1,last1), which contains all the elements betweenfirst1andlast1, including the element pointed byfirst1but not the element pointed bylast1.
要查找的范围。

first2, last2

Forward iteratorsto the initial and final positions of the sequence to be searched for. The range used is[first2,last2).
For(1), the elements in both ranges shall be of types comparable usingoperator==(with the elements of the first range as left-hand side operands, and those of the second as right-hand side operands).
要匹配的范围。

pred

Binary function that accepts two elements as arguments (one of each of the two sequences, in the same order), and returns a value convertible tobool. The returned value indicates whether the elements are considered to match in the context of this function.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.
一个二元函数。

Return value

An iterator to the first element of the last occurrence of[first2,last2)in[first1,last1).
If the sequence is not found, the function returnslast1.
最后一次匹配出现的位置。返回匹配位置的首元素。
如果找不到匹配，就返回last1.

• C++98
• C++11

If[first2,last2)is an empty range, the function returnslast1.

如果[first2,last2)是一个空的序列，返回last!.

Example

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// find_end example #include <iostream> // std::cout #include <algorithm> // std::find_end #include <vector> // std::vector bool 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; }

Edit & Run

Output:

needle1 found at position 5
needle2 found at position 3

Complexity

Up to linear incount2*(1+count1-count2), wherecountXis thedistancebetweenfirstXandlastX: Compares elements until the last matching subsequence is found.

Data races

Some (or all) of the objects in both ranges are accessed (possibly more than once).

Exceptions

Throws if any element comparison (or call topred) throws or if any of the operations on iterators throws.
Note that invalid arguments causeundefined behavior.

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author:天下无双

Email:[e-mail]

2014-9-12

于GDUT

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