stl:vector:vector_constructors

Syntax:

    #include <vector>
    vector();
    vector( const vector& c );
    vector( size_type num, const TYPE& val = TYPE() );
    vector( input_iterator start, input_iterator end );
    ~vector();

The default vector constructor takes no arguments, creates a new instance of that vector.

The second constructor is a default copy constructor that can be used to create a new vector that is a copy of the given vector c.

The third constructor creates a vector with space for num objects. If val is specified, each of those objects will be given that value. For example, the following code creates a vector consisting of five copies of the integer 42:

   vector<int> v1( 5, 42 );

The last constructor creates a vector that is initialized to contain the elements between start and end. For example:

   // create a vector of random integers
   cout << "original vector: ";
   vector<int> v;
   for( int i = 0; i < 10; ++i ) {
     int num = (int) rand() % 10;
     cout << num << " ";
     v.push_back( num );
   }
   cout << endl;
 
   // find the first element of v that is even
   vector<int>::iterator iter1 = v.begin();
   while( iter1 != v.end() && *iter1 % 2 != 0 ) {
     ++iter1;
   }
 
   // find the last element of v that is even
   vector<int>::iterator iter2 = v.end();
   do {
     --iter2;
   } while( iter2 != v.begin() && *iter2 % 2 != 0 );
 
   // only proceed if we find both numbers
   if( iter1 != v.end() && iter2 != v.begin() ) {
     cout << "first even number: " << *iter1 << ", last even number: " << *iter2 << endl;
 
     cout << "new vector: ";
     vector<int> v2( iter1, iter2 );
     for( int i = 0; i < v2.size(); ++i ) {
       cout << v2[i] << " ";
     }
     cout << endl;
   }

When run, this code displays the following output:

   original vector: 1 9 7 9 2 7 2 1 9 8
   first even number: 2, last even number: 8
   new vector: 2 7 2 1 9

All of these constructors run in linear time except the first, which runs in constant time.

The default destructor is called when the vector should be destroyed.