C++中怎么实现vector的交换?

// vector_swap.cpp
// compile with: /EHsc
#include <vector>
#include <iostream>

int main( )
{
using namespace std;
vector <int> v1, v2;

v1.push_back( 1 );
v1.push_back( 2 );
v1.push_back( 3 );

v2.push_back( 10 );
v2.push_back( 20 );

cout << "The number of elements in v1 = " << v1.size( ) << endl;
cout << "The number of elements in v2 = " << v2.size( ) << endl;
cout << endl;

v1.swap( v2 );

cout << "The number of elements in v1 = " << v1.size( ) << endl;
cout << "The number of elements in v2 = " << v2.size( ) << endl;
}