Although each kind of STL collection has a different set of behaviors, they all support ten common functions. This section describes each of these functions using a vector of t objects as a concrete example. The first group of functions construct, destroy, and perform size-related functions.

The following example illustrates each of these common functions using a vector of integers. This example makes use of a function called push_back() , which appends a copy of its argument to the end of the vector .

Example <ospace/osstd/examples/vec1.cpp>


  #include <iostream>
#include <vector>

void
main()
  {
  vector< int > v1; // Empty vector of integers.
  cout << "empty = " << v1.empty() << "\n";
  cout << "size = " << v1.size() << "\n";
  cout << "max_size = " << v1.max_size() << "\n";

  v1.push_back( 42 ); // Add an integer to the vector.
  cout << "size = " << v1.size() << "\n";
  cout << "v1[ 0 ] = " << v1[ 0 ] << "\n";
  }

empty = 1
size = 0
max_size = 1073741823
size = 1
v1[ 0 ] = 42

The next two common functions assign one collection to another and swap the contents of two collections.

vector<
    T, Allocator >& operator=( const vector< T, Allocator >&

vec )

Replaces the contents of the vector with a copy of vec .

swap

void
    swap( vector< T, Allocator >&

vec )

Swaps the contents of the vector with vec .

Following is an example illustrating these two common functions using a vector of double .

Example <ospace/osstd/examples/vec2.cpp>


  #include <iostream>
#include <vector>

void print( double_vector& vec )
  {
  for ( int i = 0; i < vec.size(); ++i )
    cout << vec[ i ] << " ";
  cout << "\n";
  }

void main()
  {
  vector< double > v1; // Empty vector of doubles.
  v1.push_back( 32.1 );
  v1.push_back( 40.5 );

  vector< double > v2; // Another empty vector of doubles.
  v2.push_back( 3.56 );
  cout << "v1 = ";
  print( v1 );
  cout << "v2 = ";
  print( v2 );

  v1.swap( v2 ); // Swap the vector's contents.
  cout << "v1 = ";
  print( v1 );
  cout << "v2 = ";
  print( v2 );

  v2 = v1; // Assign one vector to another.
  cout << "v2 = ";
  print( v2 );
  }

v1 = 32.1 40.5
v2 = 3.56
v1 = 3.56
v2 = 32.1 40.5
v2 = 3.56

There are also non-member functions that compare and exchange vector s.

bool
    operator==( const vector< T, Allocator >&

x, const vector< T, Allocator >& y )

Returns true if the vector x contains the same items in the same order as y .

bool
    operator<( const vector< T, Allocator >&

x , const vector< T, Allocator >& y )

Returns true if the vector x is lexicographically less than y .

swap

void
    swap( vector< T, Allocator >&

,
    vector< T, Allocator >&

y )

Exchanges the contents of the vector x with y .

Because the comparison operators != , > , < =, and >= can be defined in terms of == and < , STL provides template functions that define the last four operators in terms of the first two. Therefore, as long as you provide operator== and operator< for an object, the other four are provided automatically. This is true for all objects created, not just containers.

Following is an example using these operators to compare one vector of characters with another.

Example <ospace/osstd/examples/vec3.cpp>


  #include <iostream>
#include <vector>

void main()
  {
  vector< char > v1; // Empty vector of characters.
  v1.push_back( 'h' );
  v1.push_back( 'i' );
  cout << "v1 = " << v1[ 0 ] << v1[ 1 ] << "\n";

  vector< char > v2( v1 );
  v2[ 1 ] = 'o'; // Replace second character.
  cout << "v2 = " << v2[ 0 ] << v2[ 1 ] << "\n";
  cout << "( v1 == v2 ) = " << ( v1 == v2 ) << "\n";
  cout << "( v1 < v2 ) = " << ( v1 < v2 ) << "\n";
  }

v1 = hi
v2 = ho
(v1 == v2) = 0
(v1 < v2) = 1

Common Functions

Example <ospace/osstd/examples/vec1.cpp>

Example <ospace/osstd/examples/vec2.cpp>

Example <ospace/osstd/examples/vec3.cpp>