Vector用法详解

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 

 



 

 

 ->[b]非变动操作[/b]

 


 

 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