(原創) 如何列出multimap中某個key的所有value? (C/C++) (STL)

map和multimap都自帶find()，不需Generic Algorithm就可搜尋，事實上，當container和algorithm都提供方法時，應先考慮使用container自帶的方法，因為algorithm考慮到泛型，還需要經過iterator，但container自帶的方法卻是量身訂做的，所以執行速度較快。

要列出multimap中某個key的所有value，有三種方式，此範例demo如何使用這三種方式。

1#include <iostream>
10#include <map>
11#include <string>
12
13using namespace std;
14
15int main() typedef multimap<string, string> AuthorBooks;
17 AuthorBooks authorBooks;
18
19 authorBooks.insert(make_pair("Stanley B. Lippman", "C++ Primer"));
20 authorBooks.insert(make_pair("Stanley B. Lippman", "Essentail C++"));
21 authorBooks.insert(make_pair("Scott Meyers", "Effective C++"));
22 authorBooks.insert(make_pair("Andrei Alexandrescu", "Modern C++ Design"));
23
24 string searchItem = "Stanley B. Lippman";
25
26 // Find all values by key using count & find
27 AuthorBooks::size_type entries = authorBooks.count(searchItem);
28 AuthorBooks::iterator iter = authorBooks.find(searchItem);
29 for(AuthorBooks::size_type cnt = 0; cnt != entries; ++cnt)
30 cout << iter++->second << endl;
31
32 cout << endl;
33 cout << endl;
34
35 // Find all values by key using lower_bound(), upper_bound();
36 AuthorBooks::iterator beg = authorBooks.lower_bound(searchItem);
37 AuthorBooks::iterator end = authorBooks.upper_bound(searchItem);
38
39 while(beg != end)
40 cout << beg++->second << endl;
41
42 cout << endl;
43 cout << endl;
44
45 // Find all values by key using equal_range()
46 typedef AuthorBooks::iterator iterAB;
47 pair<iterAB, iterAB> pos = authorBooks.equal_range(searchItem);
48 while(pos.first != pos.second)
49 cout << pos.first++->second << endl;
50
51 return 0;
52}

除了使用count() + find()程式碼較多外，lower_bound()/upper_bound()和equal_range()程式碼都差不多長，所以沒有特別建議。