STL --> set用法

set用法

一、set和multiset基础

　　set和multiset会根据特定的排序准则，自动将元素进行排序。不同的是后者允许元素重复而前者不允许。

需要包含头文件：

#include <set>

二、创建元素

set<int> s1;    　　　　　　　　　　　　　　　　//创建空的set对象，元素类型为int，
set<const char*, strLess> s2( strLess);     //创建空的set对象，元素类型char*，比较函数对象(即排序准则)为自定义strLess
set<int> s3(s1);    　　　　　　　　　　　　　　//利用set对象s1,拷贝生成set对象s2
int iArray[] = {, , };
set<int> s4(iArray, iArray + );    　　　　　//用迭代区间[&first, &last)所指的元素，创建一个set对象
const char* szArray[] = {"hello", "dog", "bird" };
set<const char*, strLess> s5(szArray, szArray + , strLess() );    //用迭代区间[&first, &last)所指的元素，及比较函数对象strLess，创建一个set对象

三、插入元素

set<string> set1;    //empty set
set1.insert("the");   //set1 now has one element
set1.insert("and");   //set1 now has two elements
set<int> set2;    //empty set
set2.insert(iset.begin(), iset.end());       //set2 now has 10 elements

例如：

// set::insert (C++98)
#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;
  std::set<int>::iterator it;
  std::pair<std::set<int>::iterator,bool> ret;

  // set some initial values:
  for (int i=; i<=; ++i) myset.insert(i*);    // set: 10 20 30 40 50

  ret = myset.insert();               // no new element inserted

  if (ret.second==false) it=ret.first;  // "it" now points to element 20

  myset.insert (it,);                 // max efficiency inserting
  myset.insert (it,);                 // max efficiency inserting
  myset.insert (it,);                 // no max efficiency inserting

  int myints[]= {,,};              // 10 already in set, not inserted
  myset.insert (myints,myints+);

  std::cout << "myset contains:";
  for (it=myset.begin(); it!=myset.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';

  return ;
}

结果：

myset contains:          

 四、删除元素

// erasing from set
#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;
  std::set<int>::iterator it;

  // insert some values:
  for (int i=; i<; i++) myset.insert(i*);  // 10 20 30 40 50 60 70 80 90

  it = myset.begin();
  ++it;                                         // "it" points now to 20

  myset.erase (it);
  myset.erase ();

  it = myset.find ();
  myset.erase (it, myset.end());

  std::cout << "myset contains:";
  for (it=myset.begin(); it!=myset.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';

  return ;
}

结果：

myset contains:   

五、查找元素

iset.find();     //returns iterator that refers to the element with key==1
iset.find();   //returns iterator == iset.end()
iset.count();  //returns 1;
iset.count(); //returns 0;

//set_it refers to the element with key==1
set<int>::iterator set_it = iset.find();
*set_it=;         //error: keys in a set are read-only
cout<<*set_it<<endl; //ok: can read the key

例如：

// set::find
#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;
  std::set<int>::iterator it;

  // set some initial values:
  for (int i=; i<=; i++) myset.insert(i*);    // set: 10 20 30 40 50

  it=myset.find();
  myset.erase (it);
  myset.erase (myset.find());

  std::cout << "myset contains:";
  for (it=myset.begin(); it!=myset.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';

  return ;
}

结果：

myset contains:   

 六、其他

    #include <iostream>
    #include <set>
    using namespace std;  

    int main()
    {
        typedef set<int,greater<int> > IntSet;
        IntSet s1;  

        s1.insert();
        s1.insert();
        s1.insert();
        s1.insert();
        s1.insert();
        s1.insert();
        s1.insert();
        //the inserted element that has the same value with a element existed is emitted  

        copy(s1.begin(),s1.end(),ostream_iterator<int>(cout," "));
        cout << endl << endl;  

        pair<IntSet::iterator,bool> status = s1.insert();
        if(status.second)
            cout << "4 is inserted as element "
            << distance(s1.begin(),status.first) +  << endl;
        else
            cout << "4 already exists in s1" << endl;
        copy(s1.begin(),s1.end(),ostream_iterator<int>(cout," "));
        cout << endl << endl;  

        set<int>  s2(s1.begin(),s1.end());//default sort criterion is less<
        copy(s2.begin(),s2.end(),ostream_iterator<int>(cout," "));
        cout << endl << endl;
    }  

上述程序最后新产生一个set：s2，默认排序准则是less。以s1的元素作为初值。

注意：s1和s2有不同的排序准则，所以他们的型别不同，不能直接进行相互赋值或比较。

运行结果：

 already exist in s1