【C++ Primer | 10】泛型算法

 #include<iostream>
 #include<algorithm>
 #include<vector>
 #include<string>
 #include<fstream>
 using namespace std;

 void elimDups(vector<string> &words)
 {
     sort(words.begin(), words.end());
     auto unique_end = unique(words.begin(), words.end());
     words.erase(unique_end, words.end());
 }

 void display(vector<string> &words)
 {
     for (auto c : words)
         cout << c << " ";
     cout << endl;
 }

 int main()
 {
     ifstream in("test.txt");
     if (!in)
     {
         cout << "打开文件失败" << endl;
         exit();
     }

     vector<string> words;
     string str;
     while (in >> str)
         words.push_back(str);
     elimDups(words);
     display(words);
     return ;
 }

输出结果：

 定制操作

示例代码：

 #include<iostream>
 #include<algorithm>
 #include<vector>
 #include<string>
 #include<fstream>
 using namespace std;

 void elimDups(vector<string> &words)
 {
     sort(words.begin(), words.end());
     auto unique_end = unique(words.begin(), words.end());
     words.erase(unique_end, words.end());
 }

 void biggies(vector<string> &words, vector<string>::size_type sz)
 {
     elimDups(words);  //将单词按字典排序，删除重复单词
     stable_sort(words.begin(), words.end(), [](const string &a, const string &b) { return a.size() < b.size(); });
     auto wc = find_if(words.begin(), words.end(), [sz](const string &a) { return a.size() >= sz; });
     auto count = words.end() - wc;
     for_each(wc, words.end(), [](const string &s) { cout << s << " "; });
     cout << endl;
 }

 int main()
 {
     ifstream in("test.txt");
     if (!in)
     {
         cout << "打开文件失败" << endl;
         exit();
     }

     vector<string> words;
     string str;
     while (in >> str)
         words.push_back(str);
     auto sz = ;
     biggies(words, sz);
     return ;
 }

输出结果：

再探迭代器

3. 反向迭代器

 #include<iostream>
 #include<vector>
 #include<iterator>
 using namespace std;

 int main()
 {
     vector<int> vec = { , , , , , , , , ,  };
     for (auto r_iter = vec.crbegin(); r_iter != vec.crend(); ++r_iter)
         cout << *r_iter << " ";
     cout << endl;
     return ;
 }

输出结果：

 #include <iostream>
 #include <deque>
 #include <algorithm>
 #include <iterator>
 using namespace std;

 void print(int elem)
 {
     cout << elem << ' ';
 }

 int main()
 {
     deque<int> coll;
     for (int i = ; i <= ; ++i)
         coll.push_back(i);

     deque<int>::iterator pos1;
     pos1 = find(coll.begin(), coll.end(), );

     deque<int>::iterator pos2;
     pos2 = find(coll.begin(), coll.end(), );
     for_each(pos1, pos2, print);
     cout << endl;

     deque<int>::reverse_iterator rpos1(pos1);
     deque<int>::reverse_iterator rpos2(pos2);
     for_each(rpos2, rpos1, print);
     cout << endl;
     return ;
 }

输出结果：

【分析】

代码首先在一个deque中插入1到9，然后查找元素值为2和7的位置，分别赋值给迭代器pos1和pos2，然后输出，由于STL中的操作总是左开右闭的区间，即[2,7)，所以输出2 3 4 5 6，7不会输出。

接下来将迭代器转换成逆向迭代器，再次输出，对于反向迭代器，由于是反向，所以按逻辑来说它是左开右闭的（这里我尝试了rpos2为iterator.end(),rpos1为iterator.begin(),此时输出全部），即(7,2]（事实上还是左闭右开，只不过此时的左和iterator顺序一样）。所以输出6 5 4 3 2，下面的图片解释的很清楚。