【C++ Primer】【学习笔记】【第十章】关联容器之：map类型

小灰灰 2022-08-06 10:12 156阅读 0赞

使用map对象，则需要包含map头文件。在定义map对象时，必须分别指明键和值的类型。

**一、map对象的定义**

map的构造函数如下：

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      构造函数 
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      说明 
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      map&lt;k, v&gt; m; 
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    <div style="min-width:2px; background-color:inherit">
      创建一个名为m的空map对象，其键和值的类型分别为k和v。 
    </div> </td> 
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      map&lt;k, v&gt; m(m2); 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 创建m2的副本m，m与m2必须有相同的键类型和值类型。</td> 
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      map&lt;k, v&gt; m(b, e); 
    </div> </td> 
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      创建map类型的对象m，存储迭代器b和e标记的范围内所有元素的副本。元素的类型必须能转换为pair&lt;const k, v&gt;。 
    </div> </td> 
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注：对于键类型，唯一的约束就是必须支持 < 操作符。

**二、map定义的类型**

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      map类类型成员 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 说明</td> 
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      map&lt;K, V&gt;::key_type 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 在map容器中，用作索引的键的类型。</td> 
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    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:微软雅黑; font-size:14px">map&lt;K, V&gt;::mapped_type</span> 
     <br style="background-color:inherit"> 
    </div> </td> 
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      在map容器中，键所关联的值的类型。 
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     <span style="font-family:微软雅黑; font-size:14px">map&lt;K, V&gt;::value_type</span> 
     <br style="background-color:inherit"> 
    </div> </td> 
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    <div style="min-width:2px; background-color:inherit">
      一个 
     <span style="background-color:inherit">pair类型</span>，它的first元素具有 
     <span style="background-color:inherit">const&nbsp;</span>map&lt;K, V&gt;::key_type类型，而second元素则为map&lt;K, V&gt;::mapped_type类型。 
    </div> </td> 
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注：map迭代器返回value\_type类型的值，而下标操作符返回一个mapped\_type类型的值。

**三、map对象插入元素**

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      插入方法 
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      说明 
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      m.insert(e) 
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      e是map类型对应的value_type类型的值。如果键(e.first)不在m中，则插入一个值为e.second的新元素；如果键(e.first)在m中已存在，则保持m不变。该函数返回一个pair类型的对象，包含指向键为e.first元素的map迭代器，以及一个bool类型的对象，表示是否插入了该元素。 
    </div> </td> 
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      m.insert(beg, end) 
    </div> </td> 
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      beg和end是标记元素范围的迭代器，其中的元素必须为m.value_type类型的键-值对。对于这些元素，如果其键在m中不存在，则将该键对应的元素插入m。返回值为void。 
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      m.insert(iter, e) 
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    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:微软雅黑; font-size:14px">e是map类型对应的value_type类型的值。如果(e.first)不在m中，则插入一个值为e.second的新元素，并以迭代器iter为起点搜索新元素存储的位置。该函数返回一个迭代器，指向m中具有给定键的元素。</span> 
     <br style="background-color:inherit"> 
    </div> </td> 
  </tr> 
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**四、map元素的查找和访问**

**五、map元素的删除**

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      删除方法 
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      说明 
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      m.erase(k) 
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      删除m中键为k的元素。返回size_type类型的值，表示删除的元素个数。 
    </div> </td> 
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      m. 
     <span style="font-family:微软雅黑; font-size:14px">erase</span>(p) 
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      从m中删除迭代器p所指向的元素。p必须指向m中确实存在的元素，而且不能等于m.end()。返回void类型。 
    </div> </td> 
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     <span style="font-family:微软雅黑; font-size:14px">m.</span> 
     <span style="font-family:微软雅黑; font-size:14px">erase</span> 
     <span style="font-family:微软雅黑; font-size:14px">(b, e)</span> 
     <br style="background-color:inherit"> 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:67px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:微软雅黑; font-size:14px">从m中删除一段范围内的元素，b和e必须标记m中的一段有效范围：即b和e都必须指向m中的元素或最后一个元素的下一个位置。而且，b和e要么相等（此时删除的范围为空），要么b所指向的元素必须出现在e所指向的元素之前。返回void类型。</span> 
     <br style="background-color:inherit"> 
    </div> </td> 
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**六、map容器的遍历**

使用迭代器进行遍历，如：map<string, int>::const\_iterator map\_it = word\_count.begin();

注：在使用迭代器遍历map容器时，迭代器指向的元素按键的升序排列。

**习题10.9：统计单词出现的次数**

#include <iostream>
    #include <string>
    #include <utility>
    #include <vector>
    #include <map>
    using namespace std;
    
    int main()
    {
        map<string, int> word_count;
        string word;
    
        cout << "Enter some words(Ctrl + Z or Ctrl + D to end):" << endl;
    
        while (cin >> word)
        {
            ++word_count[word];
        }
    
        cout << "word\t\t" << "times" << endl;
    
        for (map<string, int>::iterator it = word_count.begin(); it != word_count.end(); ++it)
        {
            cout << it->first << "\t\t" << it->second << endl;
        }
    
        return 0;
    }

[chapter10]$ ./a.out 
    Enter some words(Ctrl + Z or Ctrl + D to end): 
    abc abc ab def 
    word times 
    ab 1 
    abc 2 
    def 1

**习题10.12：统计单词出现的次数（insert函数实现）**

#include <iostream>
    #include <string>
    #include <utility>
    #include <vector>
    #include <map>
    using namespace std;
    
    int main()
    {
        map<string, int> word_count;
        string word;
    
        cout << "Enter some words(Ctrl + Z or Ctrl + D to end):" << endl;
    
        while (cin >> word)
        {
            pair<map<string, int>::iterator, bool> ret = word_count.insert(pair<string, int>(word, 0));
            ++ret.first->second;
        }
    
        cout << "Word\t\t" << "times" << endl;
    
        for (map<string, int>::iterator it = word_count.begin(); it != word_count.end(); ++it)
        {
            cout << it->first << "\t\t" << it->second << endl;
        }
    
        return 0;
    }

[chapter10]$ ./a.out 
    Enter some words(Ctrl + Z or Ctrl + D to end): 
    aaa bbb ccc ddd aaa bbb ccc eee 
    Word times 
    aaa 2 
    bbb 2 
    ccc 2 
    ddd 1 
    eee 1

**习题10.17：单词转换**

#include <iostream>
    #include <fstream>
    #include <sstream>
    #include <string>
    #include <utility>
    #include <vector>
    #include <map>
    #include <stdexcept>
    using namespace std;
    
    ifstream & open_file(ifstream &in, const string &file)
    {
        in.close();
        in.clear();
        in.open(file.c_str());
        return in;
    }
    
    int main(int argc, char **argv)
    {
        map<string, string> trans_map;
        string key, value;
    
        if (argc != 3)
        {
            throw runtime_error("wrong number of arguments");
        }
    
        ifstream map_file;
        if (!open_file(map_file, argv[1]))
        {
            throw runtime_error("no transformation file");
        }
    
        while (map_file >> key >> value)
        {
            trans_map.insert(make_pair(key, value));
        }
    
        ifstream input;
        if (!open_file(input, argv[2]))
        {
            throw runtime_error("no input file");
        }
       
        string line;
        while (getline(input, line))
        {
            istringstream stream(line);
            string word;
            bool firstword = true;
            while (stream >> word)
            {
                map<string, string>::const_iterator map_it = trans_map.find(word);
                if (map_it != trans_map.end())
                {
                    word = map_it->second;
                }
    
                if (firstword)
                {
                    firstword = false;
                }
                else
                {
                    cout << "  ";
                }
                cout << word;
            }
            cout << endl;
        }
    
        return 0;
    }

[chapter10]$ ./a.out 
    terminate called after throwing an instance of 'std::runtime_error' 
    what(): wrong number of arguments 
    Aborted (core dumped) 
    [chapter10]$ ./a.out dic daa 
    terminate called after throwing an instance of 'std::runtime_error' 
    what(): no transformation file 
    Aborted (core dumped)
    [chapter10]$ ./a.out dict.txt aaa 
    terminate called after throwing an instance of 'std::runtime_error' 
    what(): no input file 
    Aborted (core dumped)
    [chapter10]$ cat dict.txt
    i       I
    love    LOVE
    you     YOU
    [chapter10]$ cat input.txt
    i love you
    i love you
    [chapter10]$ ./a.out dict.txt input.txt
    I  LOVE  YOU
    I  LOVE  YOU

**习题10.18：姓氏名字**

[chapter10]$ cat exercise_10.18_name.cpp
    #include <iostream>
    #include <string>
    #include <map>
    #include <vector>
    using namespace std;
    
    int main()
    {
        map<string, vector<string> > children;
        string surname, childname;
    
        // Read: Surname + childname1 + childname2 + ... + childnamen
        do
        {
            cout << "Enter surname(Ctrl + Z or Ctrl + D to end):" << endl;
            cin >> surname;
            if (!cin)
            {
                break;
            }
    
            vector<string> chd;
            pair<map<string, vector<string> >::iterator, bool> ret = children.insert(make_pair(surname, chd));
    
            if (!ret.second)
            {
                cout << "repeated surname: " << surname << endl;
                continue;
            }
    
            cout << "Enter children's name(Ctrl + Z or Ctrl + D to end):" << endl;
            while (cin >> childname)
            {
                ret.first->second.push_back(childname);
            }
            cin.clear();
        } while(cin);
    
        cin.clear();
    
        cout << "Enter a surname to search:" << endl;
        cin >> surname;
    
        map<string, vector<string> >::iterator iter = children.find(surname);
        if (iter == children.end())
        {
            cout << "no this surname: " << surname << endl;
        }
        else
        {
            cout << "children: " << endl;
            vector<string>::iterator it = iter->second.begin();
            while (it != iter->second.end())
            {
                cout << *it++ << endl;
            }
        }
    
        return 0;
    }

[chapter10]$ ./a.out
    Enter surname(Ctrl + Z or Ctrl + D to end):
    123      
    Enter children's name(Ctrl + Z or Ctrl + D to end):
    a b c d e f g
    Enter surname(Ctrl + Z or Ctrl + D to end):
    Enter a surname to search:
    123
    children:
    a
    b
    c
    d
    e
    f
    g

**习题10.19：姓氏名字生日**

#include <iostream>
    #include <string>
    #include <map>
    #include <vector>
    using namespace std;
    
    int main()
    {
        map<string, vector<pair<string, string> > > children;
        string surname, childname, birthday;
    
        // Read: Surname + childname1&birthday1 + childname2&birthday2 + ... + childnamen&birthdayn
        do
        {
            cout << "Enter surname(Ctrl + Z or Ctrl + D to end):" << endl;
            cin >> surname;
            if (!cin)
            {
                break;
            }
    
            // child's name and birthday
            vector<pair<string, string> > chd;
            pair<map<string, vector<pair<string, string> > >::iterator, bool> ret = children.insert(make_pair(surname, chd));
    
            if (!ret.second)
            {
                cout << "repeated surname: " << surname << endl;
                continue;
            }
    
            cout << "Enter children's name and birthday(Ctrl + Z or Ctrl + D to end):" << endl;
            while (cin >> childname >> birthday)
            {
                ret.first->second.push_back(make_pair(childname, birthday));
            }
            cin.clear();
        } while(cin);
    
        cin.clear();
    
        while (1)
        {
            cout << "Enter a surname to search:" << endl;
            cin >> surname;
        
            map<string, vector<pair<string, string> > >::iterator iter = children.find(surname);
            if (iter == children.end())
            {
                cout << "no this surname: " << surname << endl;
            }
            else
            {
                cout << "children\t\tbirthday" << endl;
                vector<pair<string, string> >::iterator it = iter->second.begin();
                while (it != iter->second.end())
                {
                    cout << it->first << "\t\t" << it->second << endl;
                    it++;
                }
            }
        }
    
        return 0;
    }

[chapter10]$ ./a.out 
    Enter surname(Ctrl + Z or Ctrl + D to end):
    123
    Enter children's name and birthday(Ctrl + Z or Ctrl + D to end):
    a 11111111 b 22222222
    Enter surname(Ctrl + Z or Ctrl + D to end):
    Enter a surname to search:
    123
    children                birthday
    a               11111111
    b               22222222
    Enter a surname to search:
    456
    no this surname: 456
    Enter a surname to search:
    ^C