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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、multiset
If 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; }
STL之set && multiset
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