QValueList(3qt)QValueList(3qt)NAME
QValueList - Value based template class that provides
doubly linked lists
#include <qvaluelist.h>
Public Members
QValueList ()
QValueList ( const QValueList<T> & l )
~QValueList ()
QValueList<T>& operator= ( const QValueList<T> & l )
QValueList<T> operator+ ( const QValueList<T> & l ) const
QValueList<T>& operator+= ( const QValueList<T> & l )
bool operator== ( const QValueList<T> & l ) const
bool operator!= ( const QValueList<T> & l ) const
Iterator begin ()
ConstIterator begin () const
Iterator end ()
ConstIterator end () const
Iterator fromLast ()
ConstIterator fromLast () const
bool isEmpty () const
Iterator insert ( Iterator it, const T & x )
Iterator append ( const T & x )
Iterator prepend ( const T & x )
Iterator remove ( Iterator it )
void remove ( const T & x )
T& first ()
const T& first () const
T& last ()
const T& last () const
T& operator[] ( uint i )
const T& operator[] ( uint i ) const
Iterator at ( uint i )
ConstIterator at ( uint i ) const
Iterator find ( const T & x )
ConstIterator find ( const T & x ) const
Iterator find ( Iterator it, const T & x )
ConstIterator find ( ConstIterator it, const T & x ) const
int findIndex ( const T & x ) const
uint contains ( const T & x ) const
uint count () const
void clear ()
QValueList<T>& operator+= ( const T & x )
QValueList<T>& operator<< ( const T & x )
Protected Members
void detach ()
RELATED FUNCTION DOCUMENTATION
(Note that these are not member functions.)
QDataStream& operator<< (QDataStream & s, const
QValueList<T> & l)
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QDataStream& operator>> (QDataStream & s, QValueList<T> &
l)
DESCRIPTION
The QValueList class is a value based template class that
provides doubly linked lists.
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
a copy constructor,
an assignment operator and
a default constructor, i.e. a constructor that does not
take any arguments.
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:
#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
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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() );
}
Program output:
Bill earns 50000
Steve earns 80000
Ron earns 60000
Joe earns 50000
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
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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 Qt
Template Library, for example with qHeapSort():
Example:
QValueList l;
l.append( 5 );
l.append( 8 );
l.append( 3 );
l.append( 4 );
qHeapSort( l );
See also QValueListIterator.
MEMBER FUNCTION DOCUMENTATIONQValueList::QValueList ()
Constructs an empty list.
QValueList::QValueList ( const QValueList<;T> & l )
Constructs a copy of l.
This operation costs O(1) time since QValueList is
implicit shared. The first instance applying modifications
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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.
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.
Iterator QValueList::append ( const T & x )
Inserts the value x at the end of the list.
Returns an iterator pointing at the inserted item.
See also insert() and prepend().
ConstIterator QValueList::at ( uint i ) const
Returns an iterator pointing to the item at position i in
the list, or end() if the index is out of range.
Iterator QValueList::at ( uint i )
Returns an iterator pointing to the item at position i in
the list, or end() if the index is out of range.
ConstIterator QValueList::begin () const
Returns an iterator pointing to the first element in the
list. This iterator equals end() if the list is empty;
See also first() and end().
Iterator QValueList::begin ()
Returns an iterator pointing to the first element in the
list. This iterator equals end() if the list is empty;
See also first() and end().
void QValueList::clear ()
Removes all items from the list.
See also remove().
uint QValueList::contains ( const T & x ) const
Counts and returns the number of occurrences of the value
x in the list.
uint QValueList::count () const
Returns the number of items in the list.
See also isEmpty().
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QValueList(3qt)QValueList(3qt)void QValueList::detach () [protected]
If the list does not share its data with another
QValueList instance, then nothing happens, otherwise the
function creates a new copy of this data and detaches from
the shared one. This function is called whenever the list
is modified. The implicit sharing mechanism is implemented
this way.
ConstIterator QValueList::end () const
Returns an iterator pointing behind the last element in
the list. This iterator equals begin() if the list is
empty.
See also last() and begin().
Iterator QValueList::end ()
Returns an iterator pointing behind the last element in
the list. This iterator equals begin() if the list is
empty.
See also last() and begin().
ConstIterator QValueList::find ( ConstIterator it, const T & x )
const
Finds the first occurrence of x in the list starting at
the position given by it.
Returns end() if no item did match.
ConstIterator QValueList::find ( const T & x ) const
Finds the first occurrence of x in the list.
Returns end() if no item did match.
Iterator QValueList::find ( Iterator it, const T & x )
Finds the first occurrence of x in the list starting at
the position given by it.
Returns end() if no item did match.
Iterator QValueList::find ( const T & x )
Finds the first occurrence of x in the list.
Returns end() if no item did match.
int QValueList::findIndex ( const T & x ) const
Returns the first index of the value x in the list or -1
if no such value can be found in the list.
T& QValueList::first ()
Returns a reference to the first item in the list or the
item referenced by end() if no such items exists. Please
note that you may not change the value the end() Iterator
is pointing to.
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See also begin() and last().
const T& QValueList::first () const
Returns a reference to the first item in the list or the
item referenced by end() if no such items exists.
See also begin() and last().
ConstIterator QValueList::fromLast () const
Returns an iterator pointing to the last element in the
list or end() if no such item exists.
See also last().
Iterator QValueList::fromLast ()
Returns an iterator pointing to the last element in the
list or end() if no such item exists.
See also last().
Iterator QValueList::insert ( Iterator it, const T & x )
Inserts the value x in front of the iterator it.
Returns an iterator pointing at the inserted item.
See also append() and prepend().
bool QValueList::isEmpty () const
Returns TRUE if the list is empty, i.e. count() == 0.
Returns FALSE otherwise.
See also count().
T& QValueList::last ()
Returns a reference to the last item in the list or the
item referenced by end() if no such item exists. Please
note that you may not change the value the end() Iterator
is pointing to.
See also end(), first() and fromLast().
const T& QValueList::last () const
Returns a reference to the last item in the list or the
item referenced by end() if no such item exists.
See also end(), first() and fromLast().
bool QValueList::operator!= ( const QValueList<T> & l ) const
Compares both lists.
Returns TRUE if both list are unequal.
QValueList<;T> QValueList::operator+ ( const QValueList<T> & l )
const
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Creates a new list and fills it with the elements of this
list. Then the elements of l are appended.
Returns the new list.
QValueList<;T>& QValueList::operator+= ( const QValueList<T> & l )
Adds list to this list.
Returns a reference to this list.
QValueList<;T>& QValueList::operator+= ( const T & x )
Adds the value x to the end of the list.
Returns a reference to the list.
QValueList<;T>& QValueList::operator<< ( const T & x )
Adds the value x to the end of the list.
Returns a reference to the list.
QValueList<;T>& QValueList::operator= ( const QValueList<T> & l )
Assigns 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.
bool QValueList::operator== ( const QValueList<T> & l ) const
Compares both lists.
Returns TRUE if both list are equal.
T& QValueList::operator[] ( uint i )
Returns a reference to the item with index 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 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.
const T& QValueList::operator[] ( uint i ) const
Returns a const reference to the item with index 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 i is in range
and will deliver undefined results if it does not exist.
Iterator QValueList::prepend ( const T & x )
Inserts the value x at the beginning of the list.
Returns an iterator pointing at the inserted item.
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See also insert() and append().
Iterator QValueList::remove ( Iterator it )
Removes the item at position it in the list.
Returns an iterator pointing to the item following the
removed on or end() if the last item was deleted.
See also clear().
void QValueList::remove ( const T & x )
Removes all items which have the value x.
See also clear().
RELATED FUNCTION DOCUMENTATIONQDataStream& operator<;< (QDataStream & s, const QValueList<T> &
l)
Writes a list to the stream. The type T stored in the list
must implement the streaming operator, too.
QDataStream& operator>> (QDataStream & s, QValueList<T> & l)
Reads a list from the stream. The type T stored in the
list must implement the streaming operator, too.
SEE ALSO
http://doc.trolltech.com/qvaluelist.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2001 Trolltech AS,
http://www.trolltech.com. See the license file included
in the distribution for a complete license statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports
make our job much simpler. Thank you.
In case of content or formattting problems with this
manual page, please report them to qt-bugs@trolltech.com.
Please include the name of the manual page
(qvaluelist.3qt) and the Qt version (2.3.1).
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