QMap(3qt)QMap(3qt)NAMEQMap - Value-based template class that provides a dictionary
SYNOPSIS
#include <qmap.h>
Public Members
typedef Key key_type
typedef T mapped_type
typedef QPair<const key_type, mapped_type> value_type
typedef value_type * pointer
typedef const value_type * const_pointer
typedef value_type & reference
typedef const value_type & const_reference
typedef size_t size_type
typedef QMapIterator<Key, T> iterator
typedef QMapConstIterator<Key, T> const_iterator
typedef QPair<iterator, bool> insert_pair
typedef QMapIterator<Key, T> Iterator
typedef QMapConstIterator<Key, T> ConstIterator
typedef T ValueType
QMap ()
QMap ( const QMap<Key, T> & m )
QMap ( const std::map<Key, T> & m )
~QMap ()
QMap<Key, T> & operator= ( const QMap<Key, T> & m )
QMap<Key, T> & operator= ( const std::map<Key, T> & m )
iterator begin ()
iterator end ()
const_iterator begin () const
const_iterator end () const
const_iterator constBegin () const
const_iterator constEnd () const
iterator replace ( const Key & k, const T & v )
size_type size () const
bool empty () const
QPair<iterator, bool> insert ( const value_type & x )
void erase ( iterator it )
void erase ( const key_type & k )
size_type count ( const key_type & k ) const
T & operator[] ( const Key & k )
void clear ()
iterator find ( const Key & k )
const_iterator find ( const Key & k ) const
const T & operator[] ( const Key & k ) const
bool contains ( const Key & k ) const
size_type count () const
QValueList<Key> keys () const
QValueList<T> values () const
bool isEmpty () const
iterator insert ( const Key & key, const T & value, bool overwrite =
TRUE )
void remove ( iterator it )
void remove ( const Key & k )
Protected Members
void detach ()
RELATED FUNCTION DOCUMENTATION
QDataStream & operator>> ( QDataStream & s, QMap<Key, T> & m )
QDataStream & operator<< ( QDataStream & s, const QMap<Key, T> & m )
DESCRIPTION
The QMap class is a value-based template class that provides a
dictionary.
QMap is a Qt implementation of an STL-like map container. It can be
used in your application if the standard map is not available on all
your target platforms. QMap is part of the Qt Template Library.
QMap<Key, Data> defines a template instance to create a dictionary with
keys of type Key and values of type Data. QMap does not store pointers
to the members of the map; instead, it holds a copy of every member.
For this reason, QMap is value-based, whereas QPtrList and QDict are
pointer-based.
QMap contains and manages a collection of objects of type Data with
associated key values of type Key and provides iterators that allow the
contained objects to be addressed. QMap owns the contained items.
Some classes cannot be used within a QMap. For example everything
derived from QObject and thus all classes that implement widgets. Only
values can be used in a QMap. To qualify as a value, the class must
provide
A copy constructor
An assignment operator
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.
The class used for the key requires that the operator< is implemented
to define ordering of the keys.
QMap's function naming is consistent with the other Qt classes (e.g.,
count(), isEmpty()). QMap also provides extra functions for
compatibility with STL algorithms, such as size() and empty().
Programmers already familiar with the STL map can use these the STL-
like functions if preferred.
Example:
#include <qstring.h>
#include <qmap.h>
#include <qstring.h>
class Employee
{
public:
Employee(): sn(0) {}
Employee( const QString& forename, const QString& surname, int salary )
: fn(forename), sn(surname), sal(salary)
{ }
QString forename() const { return fn; }
QString surname() const { return sn; }
int salary() const { return sal; }
void setSalary( int salary ) { sal = salary; }
private:
QString fn;
QString sn;
int sal;
};
int main(int argc, char **argv)
{
QApplication app( argc, argv );
typedef QMap<QString, Employee> EmployeeMap;
EmployeeMap map;
map["JD001"] = Employee("John", "Doe", 50000);
map["JW002"] = Employee("Jane", "Williams", 80000);
map["TJ001"] = Employee("Tom", "Jones", 60000);
Employee sasha( "Sasha", "Hind", 50000 );
map["SH001"] = sasha;
sasha.setSalary( 40000 );
EmployeeMap::Iterator it;
for ( it = map.begin(); it != map.end(); ++it ) {
printf( "%s: %s, %s earns %d\n",
it.key().latin1(),
it.data().surname().latin1(),
it.data().forename().latin1(),
it.data().salary() );
}
return 0;
}
Program output:
JD001: Doe, John earns 50000
JW002: Williams, Jane earns 80000
SH001: Hind, Sasha earns 50000
TJ001: Jones, Tom earns 60000
The latest changes to Sasha's salary did not affect the value in the
list because the map created a copy of Sasha's entry. In addition,
notice that the items are sorted alphabetically (by key) when iterating
over the map.
There are several ways to find items in a map. The begin() and end()
functions return iterators to the beginning and end of the map. The
advantage of using an iterator is that you can move forward or backward
by incrementing/decrementing the iterator. The iterator returned by
end() points to the element which is one past the last element in the
container. The past-the-end iterator is still associated with the map
it belongs to, however it is not dereferenceable; operator*() will not
return a well-defined value. If the map is empty, the iterator returned
by begin() will equal the iterator returned by end().
Another way to find an element in the map is by using the find()
function. This returns an iterator pointing to the desired item or to
the end() iterator if no such element exists.
Another approach uses the operator[]. But be warned: if the map does
not contain an entry for the element you are looking for, operator[]
inserts a default value. If you do not know that the element you are
searching for is really in the list, you should not use operator[]. The
following example illustrates this:
QMap<QString,QString> map;
map["Clinton"] = "Bill";
str << map["Clinton"] << map["Bush"] << endl;
The code fragment will print out "Clinton", "". Since the value
associated with the "Bush" key did not exist, the map inserted a
default value (in this case, an empty string). If you are not sure
whether a certain element is in the map, you should use find() and
iterators instead.
If you just want to know whether a certain key is contained in the map,
use the contains() function. In addition, count() tells you how many
keys are in the map.
It is safe to have multiple iterators at the same time. If some member
of the map is removed, only iterators pointing to the removed member
become invalid; inserting in the map does not invalidate any iterators.
Since QMap is value-based, there is no need to be concerned about
deleting items in the map. The map holds its own copies and will free
them if the corresponding member or the map itself is deleted.
QMap is implicitly shared. This means you can just make copies of the
map in time O(1). If multiple QMap instances share the same data and
one is modifying the map's data, this modifying instance makes a copy
and modifies its private copy: so it does not affect other instances.
If a QMap is being used in a multi-threaded program, you must protect
all access to the map. See QMutex.
There are a couple of ways of inserting new items into the map. One
uses the insert() method; the other uses operator[]:
QMap<QString, QString> map;
map["Clinton"] = "Bill";
map.insert( "Bush", "George" );
Items can also be removed from the map in several ways. One way is to
pass an iterator to remove(). Another way is to pass a key value to
remove(), which will delete the entry with the requested key. In
addition you can clear the entire map using the clear() method.
See also QMapIterator, Qt Template Library Classes, Implicitly and
Explicitly Shared Classes, and Non-GUI Classes.
Member Type Documentation
QMap::ConstIterator
The map's const iterator type, Qt style.
QMap::Iterator
The map's iterator type, Qt style.
QMap::ValueType
Corresponds to QPair<key_type, mapped_type>, Qt style.
QMap::const_iterator
The map's const iterator type.
QMap::const_pointer
Const pointer to value_type.
QMap::const_reference
Const reference to value_type.
QMap::iterator
The map's iterator type.
QMap::key_type
The map's key type.
QMap::mapped_type
The map's data type.
QMap::pointer
Pointer to value_type.
QMap::reference
Reference to value_type.
QMap::size_type
An unsigned integral type, used to represent various sizes.
QMap::value_type
Corresponds to QPair<key_type, mapped_type>.
MEMBER FUNCTION DOCUMENTATIONQMap::QMap ()
Constructs an empty map.
QMap::QMap ( const QMap<Key, T> & m )
Constructs a copy of m.
This operation costs O(1) time because QMap is implicitly shared. This
makes returning a QMap from a function very fast. If a shared instance
is modified, it will be copied (copy-on-write), and this takes O(n)
time.
QMap::QMap ( const std::map<Key, T> & m )
Constructs a copy of m.
QMap::~QMap ()
Destroys the map. References to the values in the map and all iterators
of this map become invalidated. Since QMap is highly tuned for
performance you won't see warnings if you use invalid iterators,
because it is not possible for an iterator to check whether it is valid
or not.
iterator QMap::begin ()
Returns an iterator pointing to the first element in the map. This
iterator equals end() if the map is empty.
The items in the map are traversed in the order defined by
operator<(Key, Key).
See also end() and QMapIterator.
const_iterator QMap::begin () const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
See also end() and QMapConstIterator.
void QMap::clear ()
Removes all items from the map.
See also remove().
const_iterator QMap::constBegin () const
Returns an iterator pointing to the first element in the map. This
iterator equals end() if the map is empty.
The items in the map are traversed in the order defined by
operator<(Key, Key).
See also constEnd() and QMapConstIterator.
const_iterator QMap::constEnd () const
The iterator returned by end() points to the element which is one past
the last element in the container. The past-the-end iterator is still
associated with the map it belongs to, but it is not dereferenceable;
operator*() will not return a well-defined value.
This iterator equals constBegin() if the map is empty.
See also constBegin() and QMapConstIterator.
bool QMap::contains ( const Key & k ) const
Returns TRUE if the map contains an item with key k; otherwise returns
FALSE.
size_type QMap::count ( const key_type & k ) const
Returns the number of items whose key is k. Since QMap does not allow
duplicate keys, the return value is always 0 or 1.
This function is provided for STL compatibility.
size_type QMap::count () const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Returns the number of items in the map.
See also isEmpty().
void QMap::detach () [protected]
If the map does not share its data with another QMap instance, nothing
happens; otherwise the function creates a new copy of this map and
detaches from the shared one. This function is called whenever the map
is modified. The implicit sharing mechanism is implemented this way.
bool QMap::empty () const
Returns TRUE if the map contains no items; otherwise returns FALSE.
This function is provided for STL compatibility. It is equivalent to
isEmpty().
See also size().
iterator QMap::end ()
The iterator returned by end() points to the element which is one past
the last element in the container. The past-the-end iterator is still
associated with the map it belongs to, but it is not dereferenceable;
operator*() will not return a well-defined value.
This iterator equals begin() if the map is empty.
See also begin() and QMapIterator.
const_iterator QMap::end () const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
void QMap::erase ( iterator it )
Removes the item associated with the iterator it from the map.
This function is provided for STL compatibility. It is equivalent to
remove().
See also clear().
void QMap::erase ( const key_type & k )
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Removes the item with the key k from the map.
iterator QMap::find ( const Key & k )
Returns an iterator pointing to the element with key k in the map.
Returns end() if no key matched.
See also QMapIterator.
const_iterator QMap::find ( const Key & k ) const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Returns an iterator pointing to the element with key k in the map.
Returns end() if no key matched.
See also QMapConstIterator.
iterator QMap::insert ( const Key & key, const T & value, bool overwrite =
TRUE )
Inserts a new item with the key, key, and a value of value. If there is
already an item whose key is key, that item's value is replaced with
value, unless overwrite is FALSE (it is TRUE by default). In this case
an iterator to this item is returned, else an iterator to the new item
is returned.
QPair<iterator, bool> QMap::insert ( const value_type & x )
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Inserts the (key, value) pair x into the map. x is a QPair whose first
element is a key to be inserted and whose second element is the
associated value to be inserted. Returns a pair whose first element is
an iterator pointing to the inserted item and whose second element is a
bool indicating TRUE if x was inserted and FALSE if it was not
inserted, e.g. because it was already present.
See also replace().
bool QMap::isEmpty () const
Returns TRUE if the map contains no items; otherwise returns FALSE.
See also count().
QValueList<Key> QMap::keys () const
Returns a list of all the keys in the map, in order.
QMap<Key, T> & QMap::operator= ( const QMap<Key, T> & m )
Assigns m to this map and returns a reference to this map.
All iterators of the current map become invalidated by this operation.
The cost of such an assignment is O(1), because QMap is implicitly
shared.
QMap<Key, T> & QMap::operator= ( const std::map<Key, T> & m )
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Assigns m to this map and returns a reference to this map.
All iterators of the current map become invalidated by this operation.
T & QMap::operator[] ( const Key & k )
Returns the value associated with the key k. If no such key is present,
an empty item is inserted with this key and a reference to the empty
item is returned.
You can use this operator both for reading and writing:
QMap<QString, QString> map;
map["Clinton"] = "Bill";
stream << map["Clinton"];
const T & QMap::operator[] ( const Key & k ) const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Warning: This function differs from the non-const version of the same
function. It will not insert an empty value if the key k does not
exist. This may lead to logic errors in your program. You should check
if the element exists before calling this function.
Returns the value associated with the key k. If no such key is present,
a reference to an empty item is returned.
void QMap::remove ( iterator it )
Removes the item associated with the iterator it from the map.
See also clear().
void QMap::remove ( const Key & k )
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Removes the item with the key k from the map.
iterator QMap::replace ( const Key & k, const T & v )
Replaces the value of the element with key k, with the value v.
See also insert() and remove().
size_type QMap::size () const
Returns the number of items in the map.
This function is provided for STL compatibility. It is equivalent to
count().
See also empty().
QValueList<T> QMap::values () const
Returns a list of all the values in the map, in key order.
RELATED FUNCTION DOCUMENTATIONQDataStream & operator<< ( QDataStream & s, const QMap<Key, T> & m )
Writes the map m to the stream s. The types Key and T must implement
the streaming operator as well.
QDataStream & operator>> ( QDataStream & s, QMap<Key, T> & m )
Reads the map m from the stream s. The types Key and T must implement
the streaming operator as well.
SEE ALSO
http://doc.trolltech.com/qmap.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
license file included in the distribution for a complete license
statement.
AUTHOR
Generated automatically from the source code.
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Trolltech AS 2 February 2007 QMap(3qt)