vector的主要函数及例题

构造

// constructing vectors
#include <iostream>
#include <vector>
using namespace std;
int main (){
  unsigned int i;
  // constructors used in the same order as described above:
  vector<int> first;                                // 空vector
  vector<int> second (4,100);                       // 4个100，{100，100，100，100}
  vector<int> third (second.begin(),second.end());  // 给定区间初始化
  vector<int> fourth (third);                       // 把vector变量third拷贝到fourth完成初始化
  vector<int> five(100);                          // 100个0，但还是写成 five(100,0) 更好
  // 也可以用数组初始化
  int myints[] = {16,2,77,29};
  vector<int> fifth (myints, myints + sizeof(myints) / sizeof(int) );
  cout << "The contents of fifth are:";
  for (i=0; i < fifth.size(); i++)
    cout << " " << fifth[i];
  cout << endl;
  return 0;
}

Output: The contents of fifth are: 16 2 77 29

赋值，= 号操作符

// vector assignment
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> first (3,0);//{0，0，0}
  vector<int> second (5,0);//{0,0,0,0,0}
  second=first; //{0,0,0}，相当于用first把second覆盖掉
  first=vector<int>();//用一个空的vector赋值
  cout << "Size of first: " << int (first.size()) << endl;
  cout << "Size of second: " << int (second.size()) << endl;
  return 0;
}

两个 int 元素向量都初始化为大小不同的零序列。 然后，将 second 分配给 first，因此现在两者相等且大小为 3。然后，将 first 分配给一个新构造的空对象，因此其大小最终为0。

vector::begin，vector::end

// vector::begin
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> myvector;
  for (int i=1; i<=5; i++) myvector.push_back(i);
  vector<int>::iterator it;
  cout << "myvector contains:";
  for ( it=myvector.begin() ; it < myvector.end(); it++ )
    cout << " " << *it;
  cout << endl;
  return 0;
}

Output: myvector contains: 1 2 3 4 5

vector::rbegin，vector::rend

// vector::rbegin/rend
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> myvector;
  for (int i=1; i<=5; i++) myvector.push_back(i);
  cout << "myvector contains:";
  vector<int>::reverse_iterator rit;
  for ( rit=myvector.rbegin() ; rit < myvector.rend(); ++rit )
    cout << " " << *rit;
  cout << endl;
  return 0;
}

Output: myvector contains: 5 4 3 2 1

vector::size

// vector::size
#include <iostream>
#include <vector>
using namespace std;

int main (){
  vector<int> myints;
  cout << "0. size: " << (int) myints.size() << endl;
  for (int i=0; i<10; i++) myints.push_back(i);
  cout << "1. size: " << (int) myints.size() << endl;
  myints.insert (myints.end(),10,100);
  cout << "2. size: " << (int) myints.size() << endl;
  myints.pop_back();
  cout << "3. size: " << (int) myints.size() << endl;
  return 0;
}

Output:
0. size: 0
1. size: 10
2. size: 20
3. size: 19 

vector::empty

// vector::empty
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> myvector;
  int sum (0);
  for (int i=1;i<=10;i++) myvector.push_back(i);
  while (!myvector.empty()){
     sum += myvector.back();
     myvector.pop_back();
  }
  cout << "total: " << sum << endl; 
  return 0;
}

Output: total: 55

vector::operator[ ]

// vector::operator[]
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> myvector (10);   // 10 zero-initialized elements
  unsigned int i;
  vector<int>::size_type sz = myvector.size();
  // assign some values:
  for (i=0; i<sz; i++) myvector[i]=i;
  // reverse vector using operator[]:
  for (i=0; i<sz/2; i++){
    int temp;
    temp = myvector[sz-1-i];
    myvector[sz-1-i]=myvector[i];
    myvector[i]=temp;
  }
  cout << "myvector contains:";
  for (i=0; i<sz; i++)
    cout << " " << myvector[i];
  cout << endl;
  return 0;
}

Output: myvector contains: 9 8 7 6 5 4 3 2 1 0

vector::front

// vector::front
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> myvector;
  myvector.push_back(77);
  myvector.push_back(16);
  // now front equals 77, and back 16
  myvector.front() -= myvector.back();
  cout << "myvector.front() is now " << myvector.front() << endl;
  return 0;
}

Output: myvector.front() is now 61

vector::back

// vector::back
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> myvector;
  myvector.push_back(10);
  while (myvector.back() != 0){
    myvector.push_back ( myvector.back() -1 );
  }
  cout << "myvector contains:";
  for (unsigned i=0; i<myvector.size() ; i++)
    cout << " " << myvector[i];
  cout << endl;
  return 0;
}

Output: myvector contains: 10 9 8 7 6 5 4 3 2 1 0

vector::push_back

// vector::push_back
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> myvector;
  int myint;
  cout << "Please enter some integers (enter 0 to end):\n";
  do {
    cin >> myint;
    myvector.push_back (myint);
  } while (myint);
  cout << "myvector stores " << (int) myvector.size() << " numbers.\n";
  return 0;
}

vector::pop_back

// vector::pop_back
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> myvector;
  int sum (0);
  myvector.push_back (100);
  myvector.push_back (200);
  myvector.push_back (300);
  while (!myvector.empty()){
    sum+=myvector.back();
    myvector.pop_back();
  }
  cout << "The elements of myvector summed " << sum << endl;
  return 0;
}

vector::insert

// inserting into a vector
#include <iostream>
#include <vector>
using namespace std;
int main (){
  vector<int> myvector (3,100);
  vector<int>::iterator it;
  it = myvector.begin();
  it = myvector.insert ( it , 200 );
  myvector.insert (it,2,300);
  // "it" no longer valid, get a new one:
  it = myvector.begin();
  vector<int> anothervector (2,400);
  myvector.insert (it+2,anothervector.begin(),anothervector.end());
  int myarray [] = { 501,502,503 };
  myvector.insert (myvector.begin(), myarray, myarray+3);
  cout << "myvector contains:";
  for (it=myvector.begin(); it<myvector.end(); it++)
    cout << " " << *it;
  cout << endl;
  return 0;
}

Output: myvector contains: 501 502 503 300 300 400 400 200 100 100 100

vector::erase

// erasing from vector
#include <iostream>
#include <vector>
using namespace std;
int main (){
  unsigned int i;
  vector<unsigned int> myvector;
  // set some values (from 1 to 10)
  for (i=1; i<=10; i++) myvector.push_back(i);
  // erase the 6th element
  myvector.erase (myvector.begin()+5);
  // erase the first 3 elements:
  myvector.erase (myvector.begin(),myvector.begin()+3);
  cout << "myvector contains:";
  for (i=0; i<myvector.size(); i++)
    cout << " " << myvector[i];
  cout << endl;
  return 0;
}

Output: myvector contains: 4 5 7 8 9 10

vector::swap

// swap vectors
#include <iostream>
#include <vector>
using namespace std;
main (){
  unsigned int i;
  vector<int> first (3,100);   // three ints with a value of 100
  vector<int> second (5,200);  // five ints with a value of 200
  first.swap(second);
  cout << "first contains:";
  for (i=0; i<first.size(); i++) cout << " " << first[i];
  cout << "\nsecond contains:";
  for (i=0; i<second.size(); i++) cout << " " << second[i];
  cout << endl;
  return 0;
}

Output: first contains: 200 200 200 200 200 second contains: 100 100 100

vector::clear

// clearing vectors
#include <iostream>
#include <vector>
using namespace std;
int main (){
  unsigned int i;
  vector<int> myvector;
  myvector.push_back (100);
  myvector.push_back (200);
  myvector.push_back (300);
  cout << "myvector contains:";
  for (i=0; i<myvector.size(); i++) cout << " " << myvector[i];
  myvector.clear();
  myvector.push_back (1101);
  myvector.push_back (2202);
  cout << "\nmyvector contains:";
  for (i=0; i<myvector.size(); i++) cout << " " << myvector[i];
  cout << endl;
  return 0;
}

Output: myvector contains: 100 200 300myvector contains: 1101 2202