# wxHashMap Class Reference
[Containers]

`#include </home/work/projects/wx/2.9/wx/interface/wx/hashmap.h>`

## Detailed Description

This is a simple, type-safe, and reasonably efficient hash map class, whose interface is a subset of the interface of STL containers.

In particular, the interface is modeled after std::map, and the various, non-standard, std::hash_map (http://www.cppreference.com/wiki/stl/map/start).

Example:

            class MyClass { ... };

            // declare a hash map with string keys and int values
            WX_DECLARE_STRING_HASH_MAP( int, MyHash5 );
            // same, with int keys and MyClass* values
            WX_DECLARE_HASH_MAP( int, MyClass*, wxIntegerHash, wxIntegerEqual, MyHash1 );
            // same, with wxString keys and int values
            WX_DECLARE_STRING_HASH_MAP( int, MyHash3 );
            // same, with wxString keys and values
            WX_DECLARE_STRING_HASH_MAP( wxString, MyHash2 );

            MyHash1 h1;
            MyHash2 h2;

            // store and retrieve values
            h1[1] = new MyClass( 1 );
            h1[10000000] = NULL;
            h1[50000] = new MyClass( 2 );
            h2["Bill"] = "ABC";
            wxString tmp = h2["Bill"];
            // since element with key "Joe" is not present, this will return
            // the default value, which is an empty string in the case of wxString
            MyClass tmp2 = h2["Joe"];

            // iterate over all the elements in the class
            MyHash2::iterator it;
            for( it = h2.begin(); it != h2.end(); ++it )
            {
                wxString key = it->first, value = it->second;
                // do something useful with key and value
            }

## Declaring new hash table types

            WX_DECLARE_STRING_HASH_MAP( VALUE_T,     // type of the values
                                        CLASSNAME ); // name of the class

Declares a hash map class named CLASSNAME, with wxString keys and VALUE_T values.

            WX_DECLARE_VOIDPTR_HASH_MAP( VALUE_T,     // type of the values
                                        CLASSNAME ); // name of the class

Declares a hash map class named CLASSNAME, with void* keys and VALUE_T values.

        WX_DECLARE_HASH_MAP( KEY_T,      // type of the keys
                             VALUE_T,    // type of the values
                             HASH_T,     // hasher
                             KEY_EQ_T,   // key equality predicate
                             CLASSNAME); // name of the class

The HASH_T and KEY_EQ_T are the types used for the hashing function and key comparison. wxWidgets provides three predefined hashing functions: `wxIntegerHash` for integer types ( int, long, short, and their unsigned counterparts ), `wxStringHash` for strings ( wxString, wxChar*, char* ), and `wxPointerHash` for any kind of pointer. Similarly three equality predicates: `wxIntegerEqual`, `wxStringEqual`, `wxPointerEqual` are provided. Using this you could declare a hash map mapping int values to wxString like this:

        WX_DECLARE_HASH_MAP( int,
                             wxString,
                             wxIntegerHash,
                             wxIntegerEqual,
                             MyHash );

        // using an user-defined class for keys
        class MyKey { ... };

        // hashing function
        class MyKeyHash
        {
        public:
            MyKeyHash() { }

            unsigned long operator()( const MyKey& k ) const
                {
                    // compute the hash
                }

            MyKeyHash& operator=(const MyKeyHash&) { return *this; }
        };

        // comparison operator
        class MyKeyEqual
        {
        public:
            MyKeyEqual() { }
            bool operator()( const MyKey& a, const MyKey& b ) const
                {
                   // compare for equality
                }

            MyKeyEqual& operator=(const MyKeyEqual&) { return *this; }
        };

        WX_DECLARE_HASH_MAP( MyKey,      // type of the keys
                             SOME_TYPE,  // any type you like
                             MyKeyHash,  // hasher
                             MyKeyEqual, // key equality predicate
                             CLASSNAME); // name of the class

## Types

In the documentation below you should replace wxHashMap with the name you used in the class declaration.

- wxHashMap::key_type: Type of the hash keys.
- wxHashMap::mapped_type: Type of the values stored in the hash map.
- wxHashMap::value_type: Equivalent to struct { key_type first; mapped_type second }.
- wxHashMap::iterator: Used to enumerate all the elements in a hash map; it is similar to a value_type*.
- wxHashMap::const_iterator: Used to enumerate all the elements in a constant hash map; it is similar to a const value_type*.
- wxHashMap::size_type: Used for sizes.
- wxHashMap::Insert_Result: The return value for insert().

## Iterators

An iterator is similar to a pointer, and so you can use the usual pointer operations: ++it ( and it++ ) to move to the next element, *it to access the element pointed to, it->first ( it->second ) to access the key ( value ) of the element pointed to.

Hash maps provide forward only iterators, this means that you can't use --it, it + 3, it1 - it2.

## Predefined hashmap types

wxWidgets defines the following hashmap types:

- wxLongToLongHashMap (uses long both for keys and values)
- wxStringToStringHashMap (uses wxString both for keys and values)

##

Library: wxBase
Category: Containers

## Public Member Functions

| wxHashMap (size_type size=10)
| The size parameter is just a hint, the table will resize automatically to preserve performance.
| wxHashMap (const wxHashMap &map)
| Copy constructor.
void | clear ()
| Removes all elements from the hash map.
size_type | count (const key_type &key) const
| Counts the number of elements with the given key present in the map.
bool | empty () const
| Returns true if the hash map does not contain any elements, false otherwise.
Insert_Result | insert (const value_type &v)
| Inserts the given value in the hash map.
mapped_type | operator[] (const key_type &key)
| Use the key as an array subscript.
size_type | size () const
| Returns the number of elements in the map.
const_iterator | begin () const
| Returns an iterator pointing at the first element of the hash map.
iterator | begin ()
| Returns an iterator pointing at the first element of the hash map.
const_iterator | end () const
| Returns an iterator pointing at the one-after-the-last element of the hash map.
iterator | end ()
| Returns an iterator pointing at the one-after-the-last element of the hash map.
size_type | erase (const key_type &key)
| Erases the element with the given key, and returns the number of elements erased (either 0 or 1).
void | erase (iterator it)
| Erases the element pointed to by the iterator.
void | erase (const_iterator it)
| Erases the element with the given key, and returns the number of elements erased (either 0 or 1).
iterator | find (const key_type &key) const
| If an element with the given key is present, the functions returns an iterator pointing at that element, otherwise an invalid iterator is returned.
const_iterator | find (const key_type &key) const
| If an element with the given key is present, the functions returns an iterator pointing at that element, otherwise an invalid iterator is returned.

List of all members.

## Constructor & Destructor Documentation

wxHashMap::wxHashMap | ( | size_type | size = `10` | ) |

The size parameter is just a hint, the table will resize automatically to preserve performance.

wxHashMap::wxHashMap | ( | const wxHashMap & | map | ) |

Copy constructor.

## Member Function Documentation

const_iterator wxHashMap::begin | ( |  | ) | const

Returns an iterator pointing at the first element of the hash map.

Please remember that hash maps do not guarantee ordering.

iterator wxHashMap::begin | ( |  | ) |

Returns an iterator pointing at the first element of the hash map.

Please remember that hash maps do not guarantee ordering.

void wxHashMap::clear | ( |  | ) |

Removes all elements from the hash map.

size_type wxHashMap::count | ( | const key_type & | key | ) | const

Counts the number of elements with the given key present in the map.

This function returns only 0 or 1.

bool wxHashMap::empty | ( |  | ) | const

Returns true if the hash map does not contain any elements, false otherwise.

const_iterator wxHashMap::end | ( |  | ) | const

Returns an iterator pointing at the one-after-the-last element of the hash map.

Please remember that hash maps do not guarantee ordering.

iterator wxHashMap::end | ( |  | ) |

Returns an iterator pointing at the one-after-the-last element of the hash map.

Please remember that hash maps do not guarantee ordering.

size_type wxHashMap::erase | ( | const key_type & | key | ) |

Erases the element with the given key, and returns the number of elements erased (either 0 or 1).

void wxHashMap::erase | ( | iterator | it | ) |

Erases the element pointed to by the iterator.

After the deletion the iterator is no longer valid and must not be used.

void wxHashMap::erase | ( | const_iterator | it | ) |

Erases the element with the given key, and returns the number of elements erased (either 0 or 1).

iterator wxHashMap::find | ( | const key_type & | key | ) | const

If an element with the given key is present, the functions returns an iterator pointing at that element, otherwise an invalid iterator is returned.

                hashmap.find( non_existent_key ) == hashmap.end()

const_iterator wxHashMap::find | ( | const key_type & | key | ) | const

If an element with the given key is present, the functions returns an iterator pointing at that element, otherwise an invalid iterator is returned.

                hashmap.find( non_existent_key ) == hashmap.end()

Insert_Result wxHashMap::insert | ( | const value_type & | v | ) |

Inserts the given value in the hash map.

The return value is equivalent to a

     std::pair<wxHashMap::iterator, bool>

The iterator points to the inserted element, the boolean value is true if v was actually inserted.

mapped_type wxHashMap::operator[] | ( | const key_type & | key | ) |

Use the key as an array subscript.

The only difference is that if the given key is not present in the hash map, an element with the default `value_type()` is inserted in the table.

size_type wxHashMap::size | ( |  | ) | const

Returns the number of elements in the map.

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