wxWidgets/docs/latex/wx/hashmap.tex

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\section{\class{wxHashMap}}\label{wxhashmap}
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.
\wxheading{Example}
\begin{verbatim}
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
}
\end{verbatim}
\wxheading{Declaring new hash table types}
\begin{verbatim}
WX_DECLARE_STRING_HASH_MAP( VALUE_T, // type of the values
CLASSNAME ); // name of the class
\end{verbatim}
Declares a hash map class named CLASSNAME, with {\tt wxString} keys
and VALUE\_T values.
\begin{verbatim}
WX_DECLARE_VOIDPTR_HASH_MAP( VALUE_T, // type of the values
CLASSNAME ); // name of the class
\end{verbatim}
Declares a hash map class named CLASSNAME, with {\tt void*} keys
and VALUE\_T values.
\begin{verbatim}
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
\end{verbatim}
The HASH\_T and KEY\_EQ\_T are the types
used for the hashing function and key comparison. wxWidgets provides
three predefined hashing functions: {\tt wxIntegerHash}
for integer types ( {\tt int}, {\tt long}, {\tt short},
and their unsigned counterparts ), {\tt wxStringHash} for strings
( {\tt wxString}, {\tt wxChar*}, {\tt char*} ), and
{\tt wxPointerHash} for any kind of pointer.
Similarly three equality predicates:
{\tt wxIntegerEqual}, {\tt wxStringEqual}, {\tt wxPointerEqual} are provided.
Using this you could declare a hash map mapping {\tt int} values
to {\tt wxString} like this:
\begin{verbatim}
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
\end{verbatim}
\latexignore{\rtfignore{\wxheading{Types}}}
In the documentation below you should replace wxHashMap with the name
you used in the class declaration.
\begin{twocollist}
\twocolitem{wxHashMap::key\_type}{Type of the hash keys}
\twocolitem{wxHashMap::mapped\_type}{Type of the values stored in the hash map}
\twocolitem{wxHashMap::value\_type}{Equivalent to
{\tt struct \{ key\_type first; mapped\_type second \};} }
\twocolitem{wxHashMap::iterator}{Used to enumerate all the elements in a hash
map; it is similar to a {\tt value\_type*}}
\twocolitem{wxHashMap::const\_iterator}{Used to enumerate all the elements
in a constant hash map; it is similar to a {\tt const value\_type*}}
\twocolitem{wxHashMap::size\_type}{Used for sizes}
\end{twocollist}
\wxheading{Iterators}
An iterator is similar to a pointer, and so you can use the usual pointer
operations: {\tt ++it} ( and {\tt it++} ) to move to the next element,
{\tt *it} to access the element pointed to, {\tt it->first}
( {\tt 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 {\tt --it}, {\tt it + 3}, {\tt it1 - it2}.
\wxheading{Include files}
<wx/hashmap.h>
\latexignore{\rtfignore{\wxheading{Members}}}
\membersection{wxHashMap::wxHashMap}\label{wxhashmapctor}
\func{}{wxHashMap}{\param{size\_type}{ size = 10}}
The size parameter is just a hint, the table will resize automatically
to preserve performance.
\func{}{wxHashMap}{\param{const wxHashMap\&}{ map}}
Copy constructor.
\membersection{wxHashMap::begin}\label{wxhashmapbegin}
\constfunc{const\_iterator}{begin}{}
\func{iterator}{begin}{}
Returns an iterator pointing at the first element of the hash map.
Please remember that hash maps do not guarantee ordering.
\membersection{wxHashMap::clear}\label{wxhashmapclear}
\func{void}{clear}{}
Removes all elements from the hash map.
\membersection{wxHashMap::count}\label{wxhashmapcount}
\constfunc{size\_type}{count}{\param{const key\_type\&}{ key}}
Counts the number of elements with the given key present in the map.
This function returns only 0 or 1.
\membersection{wxHashMap::empty}\label{wxhashmapempty}
\constfunc{bool}{empty}{}
Returns true if the hash map does not contain any elements, false otherwise.
\membersection{wxHashMap::end}\label{wxhashmapend}
\constfunc{const\_iterator}{end}{}
\func{iterator}{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.
\membersection{wxHashMap::erase}\label{wxhashmaperase}
\func{size\_type}{erase}{\param{const key\_type\&}{ key}}
Erases the element with the given key, and returns the number of elements
erased (either 0 or 1).
\func{void}{erase}{\param{iterator}{ it}}
\func{void}{erase}{\param{const\_iterator}{ it}}
Erases the element pointed to by the iterator. After the deletion
the iterator is no longer valid and must not be used.
\membersection{wxHashMap::find}\label{wxhashmapfind}
\func{iterator}{find}{\param{const key\_type\&}{ key}}
\constfunc{const\_iterator}{find}{\param{const key\_type\&}{ key}}
If an element with the given key is present, the functions returns
an iterator pointing at that element, otherwise an invalid iterator
is returned (i.e. hashmap.find( non\_existent\_key ) == hashmap.end()).
\membersection{wxHashMap::insert}\label{wxhashmapinsert}
\func{void}{insert}{\param{const value\_type\&}{ v}}
Inserts the given value in the hash map.
\membersection{wxHashMap::operator[]}\label{wxhashmapbracket}
\func{mapped\_type\&}{operator[]}{\param{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 {\tt value\_type()} is inserted in the table.
\membersection{wxHashMap::size}\label{wxhashmapsize}
\constfunc{size\_type}{size}{}
Returns the number of elements in the map.