std::set一些例子程序

#include<set>
#include<iterator>
#include<iostream>
#include <algorithm>
using namespace std;
int main()
{
    set<int> eg1;
    eg1.insert(1);
    eg1.insert(100);
    eg1.insert(5);
    eg1.insert(1); //元素1因为已经存在所以set中不会再次插入1
    eg1.insert(10);
    eg1.insert(9);
    //遍历set，可以发现元素是有序的
    set<int>::iterator set_iter=eg1.begin();
    cout<<"Set named eg1:"<<endl;
    for(;set_iter!=eg1.end();set_iter++) cout<<*set_iter<<" ";
    cout<<endl;
    //使用size()函数可以获得当前元素个数
    cout<<"Now there are "<<eg1.size()<<" elements in the set eg1"<<endl;
    if(eg1.find(200)==eg1.end())//find()函数可以查找元素是否存在
        cout<<"200 isn't in the set eg1"<<endl;

    set<int> eg2;
    for(int i=6;i<15;i++)
        eg2.insert(i);
    cout<<"Set named eg2:"<<endl;
    for(set_iter=eg2.begin(); set_iter!=eg2.end(); set_iter++)
        cout<<*set_iter<<" ";
    cout<<endl;

    //获得两个set的并
    set<int> eg3;
    cout<<"Union(两个set的并集):";
    set_union(eg1.begin(),
              eg1.end(),
              eg2.begin(),
              eg2.end(),
              insert_iterator<set<int> >(eg3, eg3.begin())
              );//注意第五个参数的形式
    copy(eg3.begin(), eg3.end(), ostream_iterator<int>(cout," "));
    cout<<endl;

    //获得两个set的交，注意进行集合操作之前接收结果的set要调用clear()函数清空一下
    eg3.clear();
    set_intersection(eg1.begin(),
                     eg1.end(),
                     eg2.begin(),
                     eg2.end(),
                     insert_iterator<set<int> >(eg3,eg3.begin())
                     );
    cout<<"Intersection:";
    copy(eg3.begin(),eg3.end(),ostream_iterator<int>(cout," "));
    cout<<endl;

    //获得两个set的差
    eg3.clear();
    set_difference(eg1.begin(),
        eg1.end(),eg2.begin(),
        eg2.end(),
        insert_iterator<set<int> >(eg3,eg3.begin())
        );
    cout<<"Difference:";
    copy(eg3.begin(),eg3.end(),ostream_iterator<int>(cout," "));
    cout<<endl;

    //获得两个set的对称差，也就是假设两个集合分别为A和B那么对称差为AUB-A∩B
    eg3.clear();
    set_symmetric_difference(eg1.begin(),eg1.end(),eg2.begin(),eg2.end(),insert_iterator<set<int> >(eg3,eg3.begin()));
    copy(eg3.begin(),eg3.end(),ostream_iterator<int>(cout," "));
    cout<<endl;

    return 0;
}

下面给出一个关键字类型为char*的示例代码

#include<iostream>
#include<iterator>
#include<set>
using namespace std;
struct ltstr
{
bool operator() (const char* s1, const char* s2) const
{
   return strcmp(s1, s2) < 0;
}
};

int main()
{
const int N = 6;
const char* a[N] = {"isomer", "ephemeral", "prosaic",
   "nugatory", "artichoke", "serif"};
const char* b[N] = {"flat", "this", "artichoke",
   "frigate", "prosaic", "isomer"};

set<const char*,ltstr> A(a, a + N);
set<const char*,ltstr> B(b, b + N);
set<const char*,ltstr> C;

cout << "Set A: ";
//copy(A.begin(), A.end(), ostream_iterator<const char*>(cout, " "));
set<const char*,ltstr>::iterator itr;
for(itr=A.begin();itr!=A.end();itr++) cout<<*itr<<" ";
cout << endl;
cout << "Set B: ";
copy(B.begin(), B.end(), ostream_iterator<const char*>(cout, " "));  
cout << endl;

cout << "Union: ";
set_union(A.begin(), A.end(), B.begin(), B.end(),
    ostream_iterator<const char*>(cout, " "),
    ltstr());  
cout << endl;

cout << "Intersection: ";
set_intersection(A.begin(), A.end(), B.begin(),B.end(),ostream_iterator<const char*>(cout," "),ltstr());
cout<<endl;
set_difference(A.begin(), A.end(), B.begin(), B.end(),inserter(C, C.begin()),ltstr());
cout << "Set C (difference of A and B): ";
copy(C.begin(), C.end(), ostream_iterator<const char*>(cout, " "));
cout <<endl;
return 0;
}

其中的ltstr也可以这样定义
class ltstr
{
        public:
        bool operator() (const char* s1,const char*s2)const
        {
                return strcmp(s1,s2)<0;
        }
};

更加通用的应用方式那就是数据类型也是由用户自定义的类来替代，比较的函数自定义，甚至可以加上二级比较，比如首先按照总分数排序，对于分数相同的按照id排序，下面是示例代码

#include<set>
#include<iostream>
using namespace std;
struct
{
                int id;
                int score;
                string name;
};
struct compare
{
        bool operator()(const Entity& e1,const Entity& e2)const   {
                if(e1.score<e2.score) return true;
                else
                        if(e1.score==e2.score)
                                if(e1.id<e2.id) return true;

                return false;
        }
};

int main()
{
        set<Entity,compare>s_test;
        Entity a,b,c;
        a.id=123;a.score=90;a.name="bill";
        b.id=121;b.score=85;b.name="mary";
        c.id=130;c.score=85;c.name="jerry";
        s_test.insert(a);s_test.insert(b);s_test.insert(c);
        set<Entity,compare>::iterator itr;
        cout<<"Score List(ordered by score):\n";
        for(itr=s_test.begin();itr!=s_test.end();itr++)
                cout<<itr->id<<"---"<<itr->name<<"---"<<itr->score<<endl;
        return 0;
}