C++ Lists

  #include <list>
  void assign( size_type num, const TYPE& val );
  void assign( input_iterator start, input_iterator end );

 vector<int> v;
 v.assign( 10, 42 );
 for( int i = 0; i < v.size(); i++ ) {
   cout << v[i] << " ";
 }
 cout << endl;            

 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( int i = 0; i < v2.size(); i++ ) {
   cout << v2[i] << " ";
 }
 cout << endl;            

 0 1 2 3 4 5 6 7 8 9            

  #include <list>
  TYPE& back();
  const TYPE& back() const;

The back() function returns a reference to the last element in the list.

For example:

 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;           

This code produces the following output:

 The first element is 0 and the last element is 4               

The back() function runs in constant time.

  #include <list>
  iterator begin();
  const_iterator begin() const;

The function begin() returns an iterator to the first element of the list. begin() should run in constant time.

For example, the following code uses begin() to initialize an iterator that is used to traverse a list:

   // Create a list of characters
   list<char> charList;
   for( int i=0; i < 10; i++ ) {
     charList.push_front( i + 65 );
   }
   // Display the list
   list<char>::iterator theIterator;
   for( theIterator = charList.begin(); theIterator != charList.end(); theIterator++ ) {
     cout << *theIterator;
   }            

  #include <list>
  void clear();

The function clear() deletes all of the elements in the list. clear() runs in linear time.

  container();  container( const container& c );  ~container();

Every list has a default constructor, copy constructor, and destructor.

The default constructor takes no arguments, creates a new instance of that list, and runs in constant time. The default copy constructor runs in linear time and can be used to create a new list that is a copy of the given list c.

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

For example, the following code creates a pointer to a vector of integers and then uses the default list constructor to allocate a memory for a new vector:

 v = new vector<int>();
		

Related topics:
Special container constructors, resize


  
  
  

  
  



  

    List constructors
  

  

    Syntax:
  
  

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

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

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

The third constructor creates a list 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 list 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 );              

 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 list should be destroyed.

  #include <list>
  list operator=(const list& c2);
  bool operator==(const list& c1, const list& c2);
  bool operator!=(const list& c1, const list& c2);
  bool operator<(const list& c1, const list& c2);
  bool operator>(const list& c1, const list& c2);
  bool operator<=(const list& c1, const list& c2);
  bool operator>=(const list& c1, const list& c2);

All of the C++ containers can be compared and assigned with the standard comparison operators: ==, !=, <=, >=, <, >, and =. Performing a comparison or assigning one list to another takes linear time.

Two lists are equal if:

1. Their size is the same, and
2. Each member in location i in one list is equal to the the member in location i in the other list.

Comparisons among lists are done lexicographically.

  #include <list>
  bool empty() const;

The empty() function returns true if the list has no elements, false otherwise.

For example, the following code uses empty() as the stopping condition on a (C/C++ Keywords) while loop to clear a list and display its contents in reverse order:

 vector<int> v;
 for( int i = 0; i < 5; i++ ) {
   v.push_back(i);
 }
 while( !v.empty() ) {
   cout << v.back() << endl;
   v.pop_back();
 }              

  #include <list>
  iterator end();
  const_iterator end() const;

The end() function returns an iterator just past the end of the list.

Note that before you can access the last element of the list using an iterator that you get from a call to end(), you'll have to decrement the iterator first.

For example, the following code uses begin() and end() to iterate through all of the members of a vector:

 vector<int> v1( 5, 789 );
 vector<int>::iterator it;
 for( it = v1.begin(); it != v1.end(); it++ ) {
   cout << *it << endl;
 }              

The iterator is initialized with a call to begin(). After the body of the loop has been executed, the iterator is incremented and tested to see if it is equal to the result of calling end(). Since end() returns an iterator pointing to an element just after the last element of the vector, the loop will only stop once all of the elements of the vector have been displayed.

end() runs in constant time.

  #include <list>
  iterator erase( iterator loc );
  iterator erase( iterator start, iterator end );

The erase() function either deletes the element at location loc, or deletes the elements between start and end (including start but not including end). The return value is the element after the last element erased.

The first version of erase (the version that deletes a single element at location loc) runs in constant time for lists and linear time for vectors, dequeues, and strings. The multiple-element version of erase always takes linear time.

For example:

 // Create a vector, load it with the first ten characters of the alphabet
 vector<char> alphaVector;
 for( int i=0; i < 10; i++ ) {
   alphaVector.push_back( i + 65 );
 }
 int size = alphaVector.size();
 vector<char>::iterator startIterator;
 vector<char>::iterator tempIterator;
 for( int i=0; i < size; i++ ) {
   startIterator = alphaVector.begin();
   alphaVector.erase( startIterator );
   // Display the vector
   for( tempIterator = alphaVector.begin(); tempIterator != alphaVector.end(); tempIterator++ ) {
     cout << *tempIterator;
   }
   cout << endl;
 }              

That code would display the following output:

 BCDEFGHIJ
 CDEFGHIJ
 DEFGHIJ
 EFGHIJ
 FGHIJ
 GHIJ
 HIJ
 IJ
 J              

In the next example, erase() is called with two iterators to delete a range of elements from a vector:

 // create a vector, load it with the first ten characters of the alphabet
 vector<char> alphaVector;
 for( int i=0; i < 10; i++ ) {
   alphaVector.push_back( i + 65 );
 }
 // display the complete vector
 for( int i = 0; i < alphaVector.size(); i++ ) {
   cout << alphaVector[i];
 }
 cout << endl;            

 // use erase to remove all but the first two and last three elements
 // of the vector
 alphaVector.erase( alphaVector.begin()+2, alphaVector.end()-3 );
 // display the modified vector
 for( int i = 0; i < alphaVector.size(); i++ ) {
   cout << alphaVector[i];
 }
 cout << endl;            

When run, the above code displays:

 ABCDEFGHIJ
 ABHIJ          

  #include <list>
  TYPE& front();
  const TYPE& front() const;

The front() function returns a reference to the first element of the list, and runs in constant time.

  #include <list>
  iterator insert( iterator loc, const TYPE& val );
  void insert( iterator loc, size_type num, const TYPE& val );
  template<TYPE> void insert( iterator loc, input_iterator start, input_iterator end );

The insert() function either:

• inserts val before loc, returning an iterator to the element inserted,
• inserts num copies of val before loc, or
• inserts the elements from start to end before loc.

For example:

 // Create a vector, load it with the first 10 characters of the alphabet
 vector<char> alphaVector;
 for( int i=0; i < 10; i++ ) {
   alphaVector.push_back( i + 65 );
 }              

 // 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;
 }              

This code would display:

 CCCCABCDEFGHIJ         

  #include <list>
  size_type max_size() const;

The max_size() function returns the maximum number of elements that the list can hold. The max_size() function should not be confused with the size() or (C++ Strings) capacity() functions, which return the number of elements currently in the list and the the number of elements that the list will be able to hold before more memory will have to be allocated, respectively.

  #include <list>
  void merge( list &lst );
  void merge( list &lst, BinPred compfunction );

The function merge() merges the list with lst, producing a combined list that is ordered with respect to the < operator. If compfunction is specified, then it is used as the comparison function for the lists instead of <.

merge() runs in linear time.

  #include <list>
  void pop_back();

The pop_back() function removes the last element of the list.

pop_back() runs in constant time.

  #include <list>
  void pop_front();

The function pop_front() removes the first element of the list.

The pop_front() function runs in constant time.

  #include <list>
  void push_back( const TYPE& val );

The push_back() function appends val to the end of the list.

For example, the following code puts 10 integers into a list:

   list<int> the_list;
   for( int i = 0; i < 10; i++ )
     the_list.push_back( i );           

When displayed, the resulting list would look like this:

 0 1 2 3 4 5 6 7 8 9            

push_back() runs in constant time.

  #include <list>
  void push_front( const TYPE& val );

The push_front() function inserts val at the beginning of list.

push_front() runs in constant time.

  #include <list>
  reverse_iterator rbegin();
  const_reverse_iterator rbegin() const;

The rbegin() function returns a reverse_iterator to the end of the current list.

rbegin() runs in constant time.

  #include <list>
  void remove( const TYPE &val );

The function remove() removes all elements that are equal to val from the list.

For example, the following code creates a list of the first 10 characters of the alphabet, then uses remove() to remove the letter 'E' from the list:

   // Create a list that has the first 10 letters of the alphabet
   list<char> charList;
   for( int i=0; i < 10; i++ )
     charList.push_front( i + 65 );
   // Remove all instances of 'E'
   charList.remove( 'E' );              

Remove runs in linear time.

  #include <list>
  void remove_if( UnPred pr );

The remove_if() function removes all elements from the list for which the unary predicate pr is true.

remove_if() runs in linear time.

  #include <list>
  reverse_iterator rend();
  const_reverse_iterator rend() const;

The function rend() returns a reverse_iterator to the beginning of the current list.

rend() runs in constant time.

  #include <list>
  void resize( size_type num, const TYPE& val = TYPE() );

The function resize() changes the size of the list to size. If val is specified then any newly-created elements will be initialized to have a value of val.

This function runs in linear time.

  #include <list>
  void reverse();

The function reverse() reverses the list, and takes linear time.

  #include <list>
  size_type size() const;

The size() function returns the number of elements in the current list.

  #include <list>
  void sort();
  void sort( BinPred p );

The sort() function is used to sort lists into ascending order. Ordering is done via the < operator, unless p is specified, in which case it is used to determine if an element is less than another.

Sorting takes N log N time.

  #include <list>
  void splice( iterator pos, list& lst );
  void splice( iterator pos, list& lst, iterator del );
  void splice( iterator pos, list& lst, iterator start, iterator end );

The splice() function inserts lst at location pos. If specified, the element(s) at del or from start to end are removed.

splice() simply moves elements from one list to another, and doesn't actually do any copying or deleting. Because of this, splice() runs in constant time.

  #include <list>
  void swap( container& from );

The swap() function exchanges the elements of the current list with those of from. This function operates in constant time.

For example, the following code uses the swap() function to exchange the values of two strings:

   string first( "This comes first" );
   string second( "And this is second" );
   first.swap( second );
   cout << first << endl;
   cout << second << endl;          

The above code displays:

   And this is second
   This comes first             

  #include <list>
  void unique();
  void unique( BinPred pr );

The function unique() removes all consecutive duplicate elements from the list. Note that only consecutive duplicates are removed, which may require that you sort() the list first.

Equality is tested using the == operator, unless pr is specified as a replacement. The ordering of the elements in a list should not change after a call to unique().

unique() runs in linear time.