STL之set && multiset

一、set在了解关联容器set之前，让我们先来看看下面这个例子，并猜测该例子输出什么：

// stl/set1.cpp

#include <iostream>
#include <set>

int main()
{
//type of the collection
typedef std::set<int> IntSet;

IntSet coll;        //set container for int values

/* insert elements from 1 to 6 in arbitray order
*- value 1 gets inserted twice
*/
coll.insert(3);
coll.insert(1);
coll.insert(5);
coll.insert(4);
coll.insert(1);
coll.insert(6);
coll.insert(2);

/* print all elements
*- iterate over all elements
*/
IntSet::const_iterator pos;
for (pos = coll.begin(); pos != coll.end(); ++pos) {
std::cout << *pos << ' ';
}
std::cout << std::endl;
}

其中，输出的结果为：1 2 3 4 5 6下面，我们根据该输出结果对关联容器set做一个分析：1. set元素的唯一性；2. set默认按照从小到大排序；This type uses the default sorting criterion, which sorts the elements by using operator <.　　如果你想要改变它的排序方法，需要传递额外的参数，例如：

typedef set<int,greater<int> > IntSet;

　　Note that you have to put a space between the two ">" characters. ">>" would be parsed as shift operator, which would result in a syntax error.二、multisetIf you want to use a multiset rather than a set, you need only change the type of the container (the header file remains the same):

typedef multiset<int> IntSet;

A multiset allows duplicates, so it would contain two elements that have value 1. Thus, the output of the program would change to the following:

1 1 2 3 4 5 6

例如：

// stl/mmap1.cpp

#include <iostream>
#include <map>
#include <string>
using namespace std;

int main()
{
//type of the collection
typedef multimap<int, string> IntStringMMap;

IntStringMMap coll;       //set container for int/string values

//insert some elements in arbitrary order
//- a value with key 1 gets inserted twice
coll.insert(make_pair(5,"tagged"));
coll.insert(make_pair(2,"a"));
coll.insert(make_pair(1,"this"));
coll.insert(make_pair(4,"of"));
coll.insert(make_pair(6,"strings"));
coll.insert(make_pair(1,"is"));
coll.insert(make_pair(3,"multimap"));

/* print all element values
*- iterate over all elements
*- element member second is the value
*/
IntStringMMap::iterator pos;
for (pos = coll.begin(); pos != coll.end(); ++pos) {
cout << pos->second << ' ';
}
cout << endl;
}