QAsciiDict Class

Qt 3.0.5

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QAsciiDict Class Reference

The QAsciiDict class is a template class that provides a dictionary based on char* keys. More...

#include <qasciidict.h>

Inherits QPtrCollection.

List of all member functions.

Public Members

QAsciiDict ( int size = 17, bool caseSensitive = TRUE, bool copyKeys = TRUE )
QAsciiDict ( const QAsciiDict<type> & dict )
~QAsciiDict ()
QAsciiDict<type> & operator= ( const QAsciiDict<type> & dict )
virtual uint count () const
uint size () const
bool isEmpty () const
void insert ( const char * key, const type * item )
void replace ( const char * key, const type * item )
bool remove ( const char * key )
type * take ( const char * key )
type * find ( const char * key ) const
type * operator[] ( const char * key ) const
virtual void clear ()
void resize ( uint newsize )
void statistics () const

Important Inherited Members

bool autoDelete () const
void setAutoDelete ( bool enable )

Protected Members

virtual QDataStream & read ( QDataStream & s, QPtrCollection::Item & item )
virtual QDataStream & write ( QDataStream & s, QPtrCollection::Item ) const

Detailed Description

The QAsciiDict class is a template class that provides a dictionary based on char* keys.

QAsciiDict is implemented as a template class. Define a template instance QAsciiDict<X> to create a dictionary that operates on pointers to X (X*).

A dictionary is a collection of key-value pairs. The key is a char* used for insertion, removal and lookup. The value is a pointer. Dictionaries provide very fast insertion and lookup.

QAsciiDict cannot handle Unicode keys; use the QDict template instead, which uses QString keys. A QDict has the same performace as a QAsciiDict.

Example:

    QAsciiDict<QLineEdit> fields;
    fields.insert( "forename", new QLineEdit( this ) );
    fields.insert( "surname", new QLineEdit( this ) );

    fields["forename"]->setText( "Homer" );
    fields["surname"]->setText( "Simpson" );

    QAsciiDictIterator<QLineEdit> it( fields ); // See QAsciiDictIterator
    for( ; it.current(); ++it )
        cout << it.currentKey() << ": " << it.current()->text() << endl;
    cout << endl;

    if ( fields["forename"] && fields["surname"] )
        cout << fields["forename"]->text() << " " 
            << fields["surname"]->text() << endl;  // Prints "Homer Simpson"

    fields.remove( "forename" ); // Does not delete the line edit
    if ( ! fields["forename"] )
        cout << "forename is not in the dictionary" << endl;

In this example we use a dictionary to keep track of the line edits we're using. We insert each line edit into the dictionary with a unique name and then access the line edits via the dictionary. See QPtrDict, QIntDict and QDict.

See QDict for full details, including the choice of dictionary size, and how deletions are handled.

Member Function Documentation

QAsciiDict::QAsciiDict ( int size = 17, bool caseSensitive = TRUE, bool copyKeys = TRUE )

Constructs a dictionary optimized for less than size entries.

We recommend setting size to a suitably large prime number (a bit larger than the expected number of entries). This makes the hash distribution better and hence the lookup faster.

When caseSensitive is TRUE (the default) QAsciiDict treats "abc" and "Abc" as different keys; when it is FALSE "abc" and "Abc" are the same. Case-insensitive comparison includes only the 26 letters in US-ASCII.

If copyKeys is TRUE (the default), the dictionary copies keys using strcpy; if it is FALSE, the dictionary just copies the pointers.

QAsciiDict::QAsciiDict ( const QAsciiDict<type> & dict )

Constructs a copy of dict.

Each item in dict is inserted into this dictionary. Only the pointers are copied (shallow copy).

QAsciiDict::~QAsciiDict ()

Removes all items from the dictionary and destroys it.

The items are deleted if auto-delete is enabled.

All iterators that access this dictionary will be reset.

bool QPtrCollection::autoDelete () const

Returns the setting of the auto-delete option. The default is FALSE.

void QAsciiDict::clear () `[virtual]`

Removes all items from the dictionary.

The removed items are deleted if auto-deletion is enabled.

All dictionary iterators that operate on dictionary are reset.

See also remove(), take() and setAutoDelete().

Reimplemented from QPtrCollection.

uint QAsciiDict::count () const `[virtual]`

Returns the number of items in the dictionary.

type * QAsciiDict::find ( const char * key ) const

Returns the item associated with key, or null if the key does not exist in the dictionary.

This function uses an internal hashing algorithm to optimize lookup.

If there are two or more items with equal keys, then the item that was most recently inserted will be found.

Equivalent to the [] operator.

Warning: Your application will crash if you call find() on an empty dictionary; you can check with isEmpty() or count(). We don't perform this check for efficiency reasons.

void QAsciiDict::insert ( const char * key, const type * item )

Inserts the key with the item into the dictionary.

The key does not have to be a unique dictionary key. If multiple items are inserted with the same key, only the last item will be visible.

Null items are not allowed.

bool QAsciiDict::isEmpty () const

Returns TRUE if the dictionary is empty, i.e. count() == 0; otherwise it returns FALSE.

QAsciiDict<type> & QAsciiDict::operator= ( const QAsciiDict<type> & dict )

Assigns dict to this dictionary and returns a reference to this dictionary.

This dictionary is first cleared and then each item in dict is inserted into this dictionary. Only the pointers are copied (shallow copy) unless newItem() has been reimplemented().

type * QAsciiDict::operator[] ( const char * key ) const

Returns the item associated with key, or null if the key does not exist in the dictionary.

This function uses an internal hashing algorithm to optimize lookup.

If there are two or more items with equal keys, then the item that was most recently inserted will be found.

Equivalent to the find() function.

Warning: Your application will crash if you call find() on an empty dictionary; you can check with isEmpty() or count(). We don't perform this check for efficiency reasons.

QDataStream & QAsciiDict::read ( QDataStream & s, QPtrCollection::Item & item ) `[virtual protected]`

Reads a dictionary item from the stream s and returns a reference to the stream.

The default implementation sets item to 0.

bool QAsciiDict::remove ( const char * key )

Removes the item associated with key from the dictionary. Returns TRUE if successful, or FALSE if the key does not exist in the dictionary.

If there are two or more items with equal keys, then the last inserted of these will be removed.

The removed item is deleted if auto-deletion is enabled.

All dictionary iterators that refer to the removed item will be set to point to the next item in the dictionary traversal order.

See also take(), clear() and setAutoDelete().

void QAsciiDict::replace ( const char * key, const type * item )

Replaces an item that has a key equal to key with item.

If the item does not already exist, it will be inserted.

Null items are not allowed.

Equivalent to:

    QAsciiDict<char> dict;
        ...
    if ( dict.find(key) )
        dict.remove( key );
    dict.insert( key, item );

If there are two or more items with equal keys, then the last inserted of these will be replaced.

void QAsciiDict::resize ( uint newsize )

Changes the size of the hashtable to newsize. The contents of the dictionary are preserved but all iterators on the dictionary become invalid.

void QPtrCollection::setAutoDelete ( bool enable )

Sets the collection to auto-delete its contents if enable is TRUE and to never delete them if enable is FALSE.

If auto-deleting is turned on, all the items in a collection are deleted when the collection itself is deleted. This is convenient if the collection has the only pointer to the items.

The default setting is FALSE, for safety. If you turn it on, be careful about copying the collection - you might find yourself with two collections deleting the same items.

Note that the auto-delete setting may also affect other functions in subclasses. For example, a subclass that has a remove() function will remove the item from its data structure, and if auto-delete is enabled, will also delete the item.

uint QAsciiDict::size () const

Returns the size of the internal hash array (as specified in the constructor).

void QAsciiDict::statistics () const

Debugging-only function that prints out the dictionary distribution using qDebug().

type * QAsciiDict::take ( const char * key )

Takes the item associated with key out of the dictionary without deleting it (even if auto-deletion is enabled).

If there are two or more items with equal keys, then the last inserted of these will be taken.

Returns a pointer to the item taken out, or null if the key does not exist in the dictionary.

All dictionary iterators that refer to the taken item will be set to point to the next item in the dictionary traversal order.

See also remove(), clear() and setAutoDelete().

QDataStream & QAsciiDict::write ( QDataStream & s, QPtrCollection::Item ) const `[virtual protected]`

Writes a dictionary item to the stream s and returns a reference to the stream.