Qt 4.7: Q3AsciiDict Class Reference

Qt Reference Documentation

# Q3AsciiDict Class Reference

The Q3AsciiDict class is a template class that provides a dictionary based on char* keys. More...

     #include <Q3AsciiDict>

This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See Porting to Qt 4 for more information.

Inherits: Q3PtrCollection.

- List of all members, including inherited members

## Public Functions

| Q3AsciiDict ( int size = 17, bool caseSensitive = true, bool copyKeys = true )
| Q3AsciiDict ( const Q3AsciiDict<type> & dict )
| ~Q3AsciiDict ()
type * | find ( const char * key ) const
void | insert ( const char * key, const type * item )
bool | isEmpty () const
bool | remove ( const char * key )
void | replace ( const char * key, const type * item )
void | resize ( uint newsize )
uint | size () const
void | statistics () const
type * | take ( const char * key )
Q3AsciiDict<type> & | operator= ( const Q3AsciiDict<type> & dict )
type * | operator[] ( const char * key ) const

## Reimplemented Public Functions

virtual void | clear ()
virtual uint | count () const

- 4 public functions inherited from Q3PtrCollection

## Protected Functions

virtual QDataStream & | read ( QDataStream & s, Q3PtrCollection::Item & item )
virtual QDataStream & | write ( QDataStream & s, Q3PtrCollection::Item item ) const

- 2 protected functions inherited from Q3PtrCollection

## Detailed Description

The Q3AsciiDict class is a template class that provides a dictionary based on char* keys.

Q3AsciiDict is implemented as a template class. Define a template instance Q3AsciiDict<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.

Q3AsciiDict cannot handle Unicode keys; use the Q3Dict template instead, which uses QString keys. A Q3Dict has the same performace as a Q3AsciiDict.

Example:

     Q3AsciiDict<QLineEdit> fields; // char* keys, QLineEdit* values
     fields.insert( "forename", new QLineEdit( this ) );
     fields.insert( "surname", new QLineEdit( this ) );

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

     Q3AsciiDictIterator<QLineEdit> it( fields ); // See Q3AsciiDictIterator
     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 Q3PtrDict, Q3IntDict and Q3Dict.

See Q3Dict for full details, including the choice of dictionary size, and how deletions are handled.

See also Q3AsciiDictIterator, Q3Dict, Q3IntDict, and Q3PtrDict.

## Member Function Documentation

### Q3AsciiDict::Q3AsciiDict ( 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 will improve lookup performance.

When caseSensitive is TRUE (the default) Q3AsciiDict treats "abc" and "Abc" as different keys; when it is FALSE "abc" and "Abc" are the same. Case-insensitive comparison only considers 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.

### Q3AsciiDict::Q3AsciiDict ( const Q3AsciiDict<type> & dict )

Constructs a copy of dict.

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

### Q3AsciiDict::~Q3AsciiDict ()

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.

See also setAutoDelete().

### void Q3AsciiDict::clear ()`[virtual]`

Reimplemented from Q3PtrCollection::clear().

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().

### uint Q3AsciiDict::count () const`[virtual]`

Reimplemented from Q3PtrCollection::count().

Returns the number of items in the dictionary.

See also isEmpty().

### type * Q3AsciiDict::find ( const char * key ) const

Returns the item associated with key, or 0 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.

See also operator[]().

### void Q3AsciiDict::insert ( const char * key, const type * item )

Inserts the key with the item into the dictionary.

Multiple items can have the same key, in which case only the last item will be accessible using operator[]().

item may not be 0.

See also replace().

### bool Q3AsciiDict::isEmpty () const

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

See also count().

### QDataStream & Q3AsciiDict::read ( QDataStream & s, Q3PtrCollection::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.

See also write().

### bool Q3AsciiDict::remove ( const char * key )

Removes the item associated with key from the dictionary. Returns TRUE if successful, i.e. if the key existed in the dictionary; otherwise returns FALSE.

If there are two or more items with equal keys, then the most recently inserted item 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 Q3AsciiDict::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.

item may not be 0.

Equivalent to:

     Q3AsciiDict<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 most recently inserted item will be replaced.

See also insert().

### void Q3AsciiDict::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.

### uint Q3AsciiDict::size () const

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

See also count().

### void Q3AsciiDict::statistics () const

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

### type * Q3AsciiDict::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 most recently inserted item will be taken.

Returns a pointer to the item taken out, or 0 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 & Q3AsciiDict::write ( QDataStream & s, Q3PtrCollection::Item item ) const`[virtual protected]`

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

See also read().

### Q3AsciiDict<type> & Q3AsciiDict::operator= ( const Q3AsciiDict<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 * Q3AsciiDict::operator[] ( const char * key ) const

Returns the item associated with key, or 0 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.

See also find().