学步园

vector

 

– 一.  vector可以模拟动态数组

 

– 二.  vector的元素可以是任意类型T，但必须具备赋值和拷贝能力（具有public

 

       拷贝构造函数和重载的赋值操作符）

 

    三.必须包含的头文件#include <vector>

 

–        四.  vector支持随机存取

 

–        五.  vector的大小（size）和容量（capacity）通常是不同的，size返回实际元素个数，

 

               capacity返回vector能容纳的元素最大数量。如果插入元素时，元素个数超过capacity，

 

       需要重新配置内部存储器。 

 

                      

 

->构造、拷贝和析构 

 

 

 

 ->非变动操作

 

 

 eg.

   vector<int> v1(10);
   cout << "The capacity of v1 is " << v1.capacity() << endl;
   cout << "The size of v1 is " << v1.size() << endl;
   vector<int> v2;
   v2.reserve(20);
   cout << "The capacity of v2 is " << v2.capacity() << endl;
   cout << "The size of v2 is " << v2.size() << endl;

output :

   The capacity of v1 is 10
   The size of v1 is 10
   The capacity of v2 is 20
   The size of v2 is 0

 

 

 

 

->赋值操作

 

 

 

所有的赋值操作都有可能调用元素类型的默认构造函数，拷贝构造函数，赋值操作符和析构函数

 

如: 

  std::list<T> l;

 

  std::vector<T> v;

 

  …

 

  v.assign(l.begin(),l.end());

eg.    

   vector<int> v;
   v.assign( 10, 42 );
   for( vector<int>::size_type i = 0; i < v.size(); i++ ) {
     cout << v[i] << " ";
   }
   cout << endl;

OutPut : 

42 42 42 42 42 42 42 42 42 42

 

   vector<int> v1;
   for( int i = 0; i < 10; i++ ) {
     v1.push_back( i );
   }
 
   vector<int> v2;
   v2.assign( v1.begin(), v1.end() );
 
   for( vector<int>::size_type i = 0; i < v2.size(); i++ ) {
     cout << v2[i] << " ";
   } 

cout << endl; 

output :

0 1 2 3 4 5 6 7 8 9  

 

元素存取 

 

 

 下面的操作是错误的:

      std::vector<T> v;//empty

 

  v[5]= t; //runtime error

 

  std::cout << v.front(); //runtime error

eg. 

  vector<string> words;

    string str;
 
    while( cin >> str ) words.push_back(str);
 
    sort( words.begin(), words.end() );
 
    cout << "In alphabetical order, the first word is '" << words.front() << "'." << endl;

假设输入是:  now is the time for all good men to come to the aid of their country

output:

In alphabetical order, the first word is 'aid'.

   vector<int> v;
   for( int i = 0; i < 5; i++ ) {
     v.push_back(i);
   }
   cout << "The first element is " << v.front()
        << " and the last element is " << v.back() << endl;

output:

The first element is 0 and the last element is 4

 

 迭代器相关函数

 

 

 

使用迭代器时应注意:

 

迭代器持续有效，除非发生以下两种情况：

 

1.) 或插入元素

 

2.) 容量变化而引起内存重新分配

 eg.

    vector<string> words;
    string str;
 
    while( cin >> str ) words.push_back(str);
 
    for( vector<string>::const_iterator iter = words.begin();
         iter != words.end(); ++iter ) {
      cout << *iter << endl;
    }

 假设输入是 :  hey mickey you're so fine 

 output:

    hey  

    mickey
    you're
    so
    fine

 

 

 

 插入（insert）元素

 

 eg.

   vector<char> alphaVector;

   for( int i=0; i < 10; i++ ) {

     alphaVector.push_back( i + 'A' );

   }

 

   











														

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