标准模板库(STL)学习指南之vector向量

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' );
   }
 
   // Insert four C's into the vector
   vector<char>::iterator theIterator = alphaVector.begin();
   alphaVector.insert( theIterator, 4, 'C' );
 
   // Display the vector
   for( theIterator = alphaVector.begin(); theIterator != alphaVector.end(); ++theIterator )    {
     cout << *theIterator;
   }

output:

CCCCABCDEFGHIJ

    vector<int> v1;
    v1.push_back( 0 );
    v1.push_back( 1 );
    v1.push_back( 2 );
    v1.push_back( 3 );
 
    vector<int> v2;
    v2.push_back( 5 );
    v2.push_back( 6 );
    v2.push_back( 7 );
    v2.push_back( 8 );
 
    cout << "Before, v2 is: ";
    for( vector<int>::size_type i = 0; i < v2.size(); i++ ) {
      cout << v2[i] << " ";
    }
    cout << endl;
 
    v2.insert( v2.end(), v1.begin(), v1.end() );
 
    cout << "After, v2 is: ";
    for( vector<int>::size_type i = 0; i < v2.size(); i++ ) {
      cout << v2[i] << " ";
    } 

   cout << endl; 

output :

    Before, v2 is: 5 6 7 8 

    After, v2 is: 5 6 7 8 0 1 2 3 

–删除（remove）元素

eg.

    vector<char> alphas;
    for( int i=0; i < 10; i++ ) {
      static const char letters[] = "ABCDEFGHIJ";
      alphas.push_back( letters[i] );
    }
    vector<char>::size_type size = alphas.size();
    vector<char>::iterator startIterator;
    vector<char>::iterator tempIterator;
    for( vector<char>::size_type i=0; i < size; i++ ) {
      startIterator = alphas.begin();
      alphas.erase( startIterator );
      // Display the vector
      for( tempIterator = alphas.begin(); tempIterator != alphas.end(); ++tempIterator ) {
        cout << *tempIterator;
      }
      cout << endl;
    }

output:

    BCDEFGHIJ
    CDEFGHIJ
    DEFGHIJ
    EFGHIJ
    FGHIJ
    GHIJ
    HIJ
    IJ 

    J

    vector<char> alphas;
    for( int i=0; i < 10; i++ ) {
      static const char letters[] = "ABCDEFGHIJ";
      alphas.push_back( letters[i] );
    }
    // display the complete vector
    for( vector<char>::size_type i = 0; i < alphas.size(); i++ ) {
      cout << alphas[i];
    }
    cout << endl;
 
    // use erase to remove all but the first two and last three elements
    // of the vector
    alphas.erase( alphas.begin()+2, alphas.end()-3 );
    // display the modified vector
    for( vector<char>::size_type i = 0; i < alphas.size(); i++ ) {
      cout << alphas[i];
    } 

    cout << endl;

output:

    ABCDEFGHIJ 

    ABHIJ 

#include <iostream>
#include <vector>
#include <iterator>
 
using namespace std;
 
int main()
{
    vector<char> alphas;
    for( int i=0; i < 10; i++ ) {
      static const char letters[] = "ABCDEFGHIJ";
      alphas.push_back( letters[i] );
    }
 
    vector<char>::iterator iter = alphas.begin();
    while( iter != alphas.end() )
    {
      if (*iter == 'B' || *iter == 'D')
        iter = alphas.erase( iter );
      else
        ++iter;
    }
 
    copy(alphas.begin(), alphas.end(), ostream_iterator<char>(cout, ""));
    cout << endl;
  } 

output :

ACEFGHIJ

转载自：http://www.cppblog.com/MiYu/archive/2010/08/31/125459.html

作者：ACShiryu 
出处：http://www.cnblogs.com/ACShiryu/ 
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