qvaluelist.doc

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/****************************************************************************
** $Id: qt/doc/qvaluelist.doc   2.3.1   edited 2001-01-26 $
**
** QValueList and QValueListIterator class documentation
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/*****************************************************************************
  QValueList documentation
 *****************************************************************************/

/*!
  \class QValueList qvaluelist.h
  \brief The QValueList class is a value based template class that provides doubly linked lists.

  \ingroup qtl
  \ingroup tools
  \ingroup shared

  Define a template instance QValueList\<X\> to create a list of values which all
  have the class X. Please notice that QValueList does not store pointers to the
  members of the list. It holds a copy of every member. That is the reason why this
  kind of classes are called "value based" while QList and QDict are "reference based".

  Some classes can not be used within a QValueList,  for example everything
  derived from QObject and thus all classes that implement widgets.
  Only values can be used in a QValueList. To qualify as a value, the class
  must provide
  <ul>
  <li>a copy constructor,
  <li>an assignment operator and
  <li> a default constructor, i.e. a constructor that does not take any arguments.
  </ul>

  Note that C++ defaults to field-by-field assignment operators and
  copy constructors if no explicit version is supplied. In many cases,
  this is sufficient.

  Example:
  \code
    #include <qvaluelist.h>
    #include <qstring.h>
    #include <stdio.h>

    class Employee
    {
    public:
	Employee(): s(0) {}
	Employee( const QString& name, int salary )
	    : n(name), s(salary)
	{}

	QString     name()   const	 	{ return n; }
	int	    salary() const	 	{ return s; }
	void	    setSalary( int salary )	{ s = salary; }
    private:
	QString     n;
	int         s;
    };

    void main()
    {
	typedef QValueList<Employee> EmployeeList;
	EmployeeList list;		// list of Employee

	list.append( Employee("Bill", 50000) );
	list.append( Employee("Steve",80000) );
	list.append( Employee("Ron",  60000) );

	Employee joe( "Joe", 50000 );
	list.append( joe );
	joe.setSalary( 4000 );
	
	EmployeeList::Iterator it;
	for( it = list.begin(); it != list.end(); ++it )
	    printf( "%s earns %d\n", (*it).name().latin1(), (*it).salary().latin1() );
    }
  \endcode

  Program output:
  \code
	Bill earns 50000
	Steve earns 80000
	Ron earns 60000
	Joe earns 50000
  \endcode

  As you can see, the latest changes to Joes salary did not affect the value
  in the list because the list created a copy of Joes entry.

  There are three ways of finding items in the list. The first one is by using
  the at() function. It returns an iterator. The advantages of
  getting an iterator is that you can now move forward or backward from this
  position by incrementing/decrementing the iterator. To get the amount of
  items in the list call count(). Valid indices are 0..count().

  The second way of accessing a list is with operator[]. That means you can address
  it like an array. The return value is a reference to the value stored in the list.
  There exist two versions of this operator. The first one is const and returns a
  const reference to the value. The second on is non const and returns a non const
  reference to the value. It is up to your compiler to choose the correct one.

  The third method is to use the functions begin() and end().
  With a simple for loop as shown in the example you can iterate over the complete list.
  It is save to have multiple iterators at the same time. If some member of the list is
  removed then only iterators pointing to the removed member become invalid. Inserting in
  the list does not invalidate any iterator. For convenience the function last() returns
  an iterator for the last and first() for the first element in the list.

  In addition you can search items in the list with the find() function. It exists in a const
  and a non const version. It starts searching from the beginning of the list, but another
  flavor of the find() function allows you to specify where searching should start.
  If you just want to know wether a certain item is at least once in the list, then you
  can use the contains() function.

  Since QValueList is value based there is no need to care about deleting elements in the
  list. The list holds its own copies and will free them if the corresponding member or
  the list itself is deleted. You can force the list to free all of its item with clear().

  QValueList is implicitly shared. That means you can just make copies of the list
  in time O(1). If multiple QValueList instances share the same data and one
  is doing a modification of the lists data then this modifying instance makes a copy
  and modifies its private copy. So it does not affect the other instances.
  From a developers point of view you can think that a QValueList and a copy of this
  list have nothing to do with each other. Developers may only notice that copying is
  very fast. People known to a CPUs MMU architecture will know this pattern as "copy on write".

  There exist three functions to insert items in the list. append()
  inserts an item at the end, prepend() inserts at the beginning
  and insert() inserts in front of the position given by an iterator.

  Items can be removed from the list in two ways. The first is to pass an iterator to
  the remove(). The other possibility is to pass a value to remove() which will
  delete all members which match this value.

  Lists can be sorted with the algorithms provided by the <a
  href="qtl.html">Qt Template Library</a>, for example with
  qHeapSort():

  Example:
  \code
	  QValueList l;
	  l.append( 5 );
	  l.append( 8 );
	  l.append( 3 );
	  l.append( 4 );
	  qHeapSort( l );
  \endcode

  \sa QValueListIterator
*/


/*!
  \fn QValueList::QValueList()
  Constructs an empty list.
*/

/*!
  \fn QValueList::QValueList( const QValueList<T>& l )
  Constructs a copy of \e l.

  This operation costs O(1) time since QValueList is implicit shared.
  The first instance applying modifications to a shared list will create
  a copy which takes in turn O(n) time. However returning a QValueList from
  a function is very fast.
*/

/*!
  \fn QValueList::~QValueList()
  Destroys the list. References to the values in the list and all iterators
  of this list become invalidated. Since QValueList is highly tuned for performance
  you wont see warnings if you use invalid iterators,
  because it is impossible for
  an iterator to check wether it is valid or not.
*/

/*!
  \fn QValueList<T>& QValueList::operator= ( const QValueList<T>& l )
  Assigns \e l to this list and returns a reference to this list.

  All iterators of the current list become invalidated by this operation.
  The cost of such an assignment is O(1) since QValueList is implicitly shared.
*/

/*!
  \fn QValueList<T> QValueList::operator+ ( const QValueList<T>& l ) const
  Creates a new list and fills it with the elements of this list. Then the
  elements of \e l are appended.

  Returns the new list.
*/

/*!
  \fn QValueList<T>& QValueList::operator+= ( const QValueList<T>& l )
  Adds \e list to this list.

  Returns a reference to this list.
*/

/*!
  \fn bool QValueList::operator== ( const QValueList<T>& l ) const
  Compares both lists.

  Returns TRUE if both list are equal.
*/

/*!
  \fn bool QValueList::operator!= ( const QValueList<T>& l ) const
  Compares both lists.

  Returns TRUE if both list are unequal.
*/

/*!
  \fn QValueList<T>& QValueList::operator+= ( const T& x )
  Adds the value \e x to the end of the list.

  Returns a reference to the list.
*/

/*!
  \fn QValueList<T>& QValueList::operator<< ( const T& x )
  Adds the value \e x to the end of the list.

  Returns a reference to the list.
*/

/*!
  \fn const T& QValueList::operator[] ( uint i ) const
  Returns a const reference to the item with index \e i in the list.
  It is up to you to check wether this item really exists. You can do that easily
  with the count() function. However this operator does not check wether \e i
  is in range and will deliver undefined results if it does not exist.
*/

/*!
  \fn T& QValueList::operator[] ( uint i )
  Returns a reference to the item with index \e i in the list.
  It is up to you to check wether this item really exists. You can do that easily
  with the count() function. However this operator does not check wether \e i
  is in range and will deliver undefined results if it does not exist.
  In contrast to the const operator[] you may manipulate the value returned by this
  operator.
*/

/*!
  \fn uint QValueList::count() const
  Returns the number of items in the list.
  \sa isEmpty()
*/

/*!
  \fn bool QValueList::isEmpty() const
  Returns TRUE if the list is empty, i.e. count() == 0. Returns FALSE
   otherwise.
  \sa count()
*/

/*!
  \fn Iterator QValueList::insert( Iterator it, const T& x )
  Inserts the value \e x in front of the iterator \e it.

  Returns an iterator pointing at the inserted item.

  \sa append(), prepend()
*/

/*!
  \fn Iterator QValueList::append( const T& x )
  Inserts the value \e x at the end of the list.

  Returns an iterator pointing at the inserted item.

  \sa insert(), prepend()
*/

/*!
  \fn Iterator QValueList::prepend( const T& x )
  Inserts the value \e x at the beginning of the list.

  Returns an iterator pointing at the inserted item.

  \sa insert(), append()
*/

/*!
  \fn Iterator QValueList::remove( Iterator it )
  Removes the item at position \e it in the list.

  Returns an iterator pointing to the item following the
  removed on or end() if the last item was deleted.

  \sa clear()
*/

/*!
  \fn void QValueList::remove( const T& x )
  Removes all items which have the value \e x.

  \sa clear()
*/

/*!
  \fn void QValueList::clear()
  Removes all items from the list.

  \sa remove()
*/

/*!
  \fn Iterator QValueList::find( const T& x )
  Finds the first occurrence of \e x in the list.

  Returns end() if no item did match.
*/

/*!
  \fn ConstIterator QValueList::find( const T& x ) const
  Finds the first occurrence of \e x in the list.

  Returns end() if no item did match.
*/

/*!
  \fn Iterator QValueList::find( Iterator it, const T& x )
  Finds the first occurrence of \e x in the list starting at
  the position given by \e it.

  Returns end() if no item did match.
*/

/*!
  \fn ConstIterator QValueList::find( ConstIterator it, const T& x ) const
  Finds the first occurrence of \e x in the list starting at
  the position given by \e it.

  Returns end() if no item did match.
*/

/*!
  \fn uint QValueList::contains( const T& x ) const
  Counts and returns the number of occurrences of the value \e x in the list.
*/

/*!
  \fn int QValueList::findIndex( const T& x ) const
  Returns the first index of the value \e x in the list or -1 if no such value
  can be found in the list.
*/

/*!
  \fn Iterator QValueList::at( uint i )
  Returns an iterator pointing to the item at position \e i in the list, or
  end() if the index is out of range.
*/

/*!