Qore::HashKeyReverseIterator Class Reference

This class an iterator class for hashes. More...

Inheritance diagram for Qore::HashKeyReverseIterator:

Public Member Methods
	constructor (hash< auto > h)
	Creates the hash iterator object. More...
	constructor ()
	Creates an empty iterator object. More...
	copy ()
	Creates a copy of the HashKeyReverseIterator object, iterating the same object as the original and in the same position. More...
string	getValue ()
	returns the current key value or throws an INVALID-ITERATOR exception if the iterator is invalid More...
Public Member Methods inherited from Qore::HashReverseIterator
	constructor (hash< auto > h)
	Creates the hash iterator object. More...
	constructor ()
	Creates an empty iterator object. More...
	copy ()
	Creates a copy of the HashReverseIterator object, iterating the same object as the original and in the same position. More...
bool	first ()
	returns True if on the last element of the hash More...
bool	last ()
	returns True if on the first element of the hash More...
bool	next ()
	Moves the current position to the previous element in the hash; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the last element in the hash if the hash is not empty. More...
bool	prev ()
	Moves the current position to the next element in the hash; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the first element in the hash if the hash is not empty. More...
Public Member Methods inherited from Qore::HashIterator
	constructor (hash< auto > h)
	Creates the hash iterator object. More...
	constructor ()
	Creates an empty hash iterator object. More...
	copy ()
	Creates a copy of the HashIterator object, iterating the same object as the original and in the same position. More...
bool	empty ()
	returns True if the hash is empty; False if not More...
string	getKey ()
	returns the current key value or throws an INVALID-ITERATOR exception if the iterator is invalid More...
auto	getKeyValue ()
	returns the current value of the current hash key being iterated or throws an INVALID-ITERATOR exception if the iterator is invalid More...
hash< auto >	getValuePair ()
	returns a hash with the current key and value (a hash with 2 keys: "key" and "value") or throws an INVALID-ITERATOR exception if the iterator is invalid More...
	reset ()
	Reset the iterator instance to its initial state. More...
bool	valid ()
	returns True if the iterator is currently pointing at a valid element, False if not More...

Detailed Description

This class an iterator class for hashes.

Call HashKeyReverseIterator::next() to iterate through the hash in reverse order; do not use the iterator if HashKeyReverseIterator::next() returns False. A hash can be iterated in reverse order by calling HashKeyReverseIterator::prev() instead of HashKeyReverseIterator::next()

Example: HashKeyReverseIterator basic usage

hash<auto> data = {
    "key1" : 1,
    "key2" : 2,
    "key3" : 3,
};
 
HashKeyReverseIterator it(data);
while (it.next()) {
    printf("iter: %n\n", it.getValue());
}
 
iter: "key3"
iter: "key2"
iter: "key1"

Note

• In general, the HashKeyReverseIterator class is not designed to be accessed from multiple threads; it was created without locking for fast and efficient use when used from a single thread. For methods that would be unsafe to use in another thread, any use of such methods in threads other than the thread where the constructor was called will cause an ITERATOR-THREAD-ERROR to be thrown.
• HashKeyReverseIterator is functionally equivalent to HashKeyIterator, but the effect of HashKeyReverseIterator::next() and HashKeyReverseIterator::prev() are the opposite of HashKeyIterator::next() and HashKeyIterator::prev(); that is HashKeyReverseIterator::next() will iterate through the hash in reverse order, while HashKeyReverseIterator::prev() iterates in forward order. Additionally the meanings of the return values for HashKeyReverseIterator::first() and HashKeyReverseIterator::last() are swapped in respect to HashKeyIterator::first() and HashKeyIterator::last().

See also

HashKeyIterator

Member Function Documentation

constructor() [1/2]

Qore::HashKeyReverseIterator::constructor

(

)

Creates an empty iterator object.

Example:

*hash<auto> h = get_hash_or_nothing();
HashKeyReverseIterator hi(h);

constructor() [2/2]

Qore::HashKeyReverseIterator::constructor

(

hash< auto >

h

)

Creates the hash iterator object.

Parameters

h	the hash to iterate

Example:

HashKeyReverseIterator hi(h);

copy()

Qore::HashKeyReverseIterator::copy

(

)

Creates a copy of the HashKeyReverseIterator object, iterating the same object as the original and in the same position.

Example:

HashKeyReverseIterator ni = i.copy();

getValue()

string Qore::HashKeyReverseIterator::getValue ( )

virtual

returns the current key value or throws an INVALID-ITERATOR exception if the iterator is invalid

Returns

the current key value or throws an INVALID-ITERATOR exception if the iterator is invalid

Code Flags:

RET_VALUE_ONLY

Example:

HashKeyReverseIterator hi(hash);
while (hi.next())
    printf("key: %s\n", hi.getValue());

Exceptions

INVALID-ITERATOR	the iterator is not pointing at a valid element
ITERATOR-THREAD-ERROR	this exception is thrown if this method is called from any thread other than the thread that created the object

Reimplemented from Qore::HashIterator.