array.tex

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%% Name:        array.tex
%% Purpose:     wxArray
%% Author:      wxWidgets Team
%% Modified by:
%% Created:
%% RCS-ID:      $Id: array.tex,v 1.35 2006/07/02 01:28:35 VZ Exp $
%% Copyright:   (c) wxWidgets Team
%% License:     wxWindows license
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\section{\class{wxArray}}\label{wxarray}

This section describes the so called {\it dynamic arrays}. This is a C
array-like data structure i.e. the member access time is constant (and not
linear according to the number of container elements as for linked lists). However, these
arrays are dynamic in the sense that they will automatically allocate more
memory if there is not enough of it for adding a new element. They also perform
range checking on the index values but in debug mode only, so please be sure to
compile your application in debug mode to use it (see \helpref{debugging overview}{debuggingoverview} for
details). So, unlike the arrays in some other
languages, attempt to access an element beyond the arrays bound doesn't
automatically expand the array but provokes an assertion failure instead in
debug build and does nothing (except possibly crashing your program) in the
release build.

The array classes were designed to be reasonably efficient, both in terms of
run-time speed and memory consumption and the executable size. The speed of
array item access is, of course, constant (independent of the number of elements)
making them much more efficient than linked lists (\helpref{wxList}{wxlist}).
Adding items to the arrays is also implemented in more or less constant time -
but the price is preallocating the memory in advance. In the \helpref{memory management}{wxarraymemorymanagement} section
you may find some useful hints about optimizing wxArray memory usage. As for executable size, all
wxArray functions are inline, so they do not take {\it any space at all}.

wxWidgets has three different kinds of array. All of them derive from
wxBaseArray class which works with untyped data and can not be used directly.
The standard macros WX\_DEFINE\_ARRAY(), WX\_DEFINE\_SORTED\_ARRAY() and
WX\_DEFINE\_OBJARRAY() are used to define a new class deriving from it. The
classes declared will be called in this documentation wxArray, wxSortedArray and
wxObjArray but you should keep in mind that no classes with such names actually
exist, each time you use one of WX\_DEFINE\_XXXARRAY macro you define a class
with a new name. In fact, these names are "template" names and each usage of one
of the macros mentioned above creates a template specialization for the given
element type.

wxArray is suitable for storing integer types and pointers which it does not
treat as objects in any way, i.e. the element pointed to by the pointer is not
deleted when the element is removed from the array. It should be noted that
all of wxArray's functions are inline, so it costs strictly nothing to define as
many array types as you want (either in terms of the executable size or the
speed) as long as at least one of them is defined and this is always the case
because wxArrays are used by wxWidgets internally. This class has one serious
limitation: it can only be used for storing integral types (bool, char, short,
int, long and their unsigned variants) or pointers (of any kind). An attempt
to use with objects of sizeof() greater than sizeof(long) will provoke a
runtime assertion failure, however declaring a wxArray of floats will not (on
the machines where sizeof(float) <= sizeof(long)), yet it will {\bf not} work,
please use wxObjArray for storing floats and doubles (NB: a more efficient
wxArrayDouble class is scheduled for the next release of wxWidgets).

wxSortedArray is a wxArray variant which should be used when searching in the
array is a frequently used operation. It requires you to define an additional
function for comparing two elements of the array element type and always stores
its items in the sorted order (according to this function). Thus, it is
 \helpref{Index()}{wxarrayindex} function execution time is $O(log(N))$ instead of
$O(N)$ for the usual arrays but the \helpref{Add()}{wxarrayadd} method is
slower: it is $O(log(N))$ instead of constant time (neglecting time spent in
memory allocation routine). However, in a usual situation elements are added to
an array much less often than searched inside it, so wxSortedArray may lead to
huge performance improvements compared to wxArray. Finally, it should be
noticed that, as wxArray, wxSortedArray can be only used for storing integral
types or pointers.

wxObjArray class treats its elements like "objects". It may delete them when
they are removed from the array (invoking the correct destructor) and copies
them using the objects copy constructor. In order to implement this behaviour
the definition of the wxObjArray arrays is split in two parts: first, you should
declare the new wxObjArray class using WX\_DECLARE\_OBJARRAY() macro and then
you must include the file defining the implementation of template type:
<wx/arrimpl.cpp> and define the array class with WX\_DEFINE\_OBJARRAY() macro
from a point where the full (as opposed to `forward') declaration of the array
elements class is in scope. As it probably sounds very complicated here is an
example:

\begin{verbatim}
#include <wx/dynarray.h>

// we must forward declare the array because it is used inside the class
// declaration
class MyDirectory;
class MyFile;

// this defines two new types: ArrayOfDirectories and ArrayOfFiles which can be
// now used as shown below
WX_DECLARE_OBJARRAY(MyDirectory, ArrayOfDirectories);
WX_DECLARE_OBJARRAY(MyFile,      ArrayOfFiles);

class MyDirectory
{
...
    ArrayOfDirectories m_subdirectories; // all subdirectories
    ArrayOfFiles       m_files;          // all files in this directory
};

...

// now that we have MyDirectory declaration in scope we may finish the
// definition of ArrayOfDirectories -- note that this expands into some C++
// code and so should only be compiled once (i.e., don't put this in the
// header, but into a source file or you will get linking errors)
#include <wx/arrimpl.cpp> // this is a magic incantation which must be done!
WX_DEFINE_OBJARRAY(ArrayOfDirectories);

// that's all!
\end{verbatim}

It is not as elegant as writing

\begin{verbatim}
typedef std::vector<MyDirectory> ArrayOfDirectories;
\end{verbatim}

but is not that complicated and allows the code to be compiled with any, however
dumb, C++ compiler in the world.

Things are much simpler for wxArray and wxSortedArray however: it is enough
just to write

\begin{verbatim}
WX_DEFINE_ARRAY(int, ArrayOfDirectories);
WX_DEFINE_SORTED_ARRAY(int, ArrayOfFiles);
\end{verbatim}

i.e. there is only one {\tt DEFINE} macro and no need for separate
{\tt DECLARE} one.


\wxheading{See also:}

\helpref{Container classes overview}{wxcontaineroverview}, \helpref{wxList}{wxlist}

\wxheading{Include files}

<wx/dynarray.h> for wxArray and wxSortedArray and additionally <wx/arrimpl.cpp>
for wxObjArray.

\latexignore{\rtfignore{\wxheading{Function groups}}}

\membersection{Macros for template array definition}\label{arraymacros}

To use an array you must first define the array class. This is done with the
help of the macros in this section. The class of array elements must be (at
least) forward declared for WX\_DEFINE\_ARRAY, WX\_DEFINE\_SORTED\_ARRAY and
WX\_DECLARE\_OBJARRAY macros and must be fully declared before you use
WX\_DEFINE\_OBJARRAY macro.

\helpref{WX\_DEFINE\_ARRAY}{wxdefinearray}\\
\helpref{WX\_DEFINE\_EXPORTED\_ARRAY}{wxdefinearray}\\
\helpref{WX\_DEFINE\_USER\_EXPORTED\_ARRAY}{wxdefinearray}\\
\helpref{WX\_DEFINE\_SORTED\_ARRAY}{wxdefinesortedarray}\\
\helpref{WX\_DEFINE\_SORTED\_EXPORTED\_ARRAY}{wxdefinesortedarray}\\
\helpref{WX\_DEFINE\_SORTED\_USER\_EXPORTED\_ARRAY}{wxdefinesortedarray}\\
\helpref{WX\_DECLARE\_EXPORTED\_OBJARRAY}{wxdeclareobjarray}\\
\helpref{WX\_DECLARE\_USER\_EXPORTED\_OBJARRAY}{wxdeclareobjarray}\\
\helpref{WX\_DEFINE\_OBJARRAY}{wxdefineobjarray}\\
\helpref{WX\_DEFINE\_EXPORTED\_OBJARRAY}{wxdefineobjarray}\\
\helpref{WX\_DEFINE\_USER\_EXPORTED\_OBJARRAY}{wxdefineobjarray}

To slightly complicate the matters even further, the operator $->$ defined by
default for the array iterators by these macros only makes sense if the array
element type is not a pointer itself and, although it still works, this
provokes warnings from some compilers and to avoid them you should use the
{\tt \_PTR} versions of the macros above. For example, to define an array of
pointers to {\tt double} you should use:

\begin{verbatim}
WX_DEFINE_ARRAY_PTR(double *, MyArrayOfDoublePointers);
\end{verbatim}

Note that the above macros are generally only useful for
wxObject types.  There are separate macros for declaring an array of a simple type,
such as an int.

The following simple types are supported:\\
int\\
long\\
size\_t\\
double

To create an array of a simple type, simply append the type you want in CAPS to
the array definition.

For example, for an integer array, you'd use one of the following variants:

\helpref{WX\_DEFINE\_ARRAY\_INT}{wxdefinearray}\\
\helpref{WX\_DEFINE\_EXPORTED\_ARRAY\_INT}{wxdefinearray}\\
\helpref{WX\_DEFINE\_USER\_EXPORTED\_ARRAY\_INT}{wxdefinearray}\\
\helpref{WX\_DEFINE\_SORTED\_ARRAY\_INT}{wxdefinesortedarray}\\
\helpref{WX\_DEFINE\_SORTED\_EXPORTED\_ARRAY\_INT}{wxdefinesortedarray}\\
\helpref{WX\_DEFINE\_SORTED\_USER\_EXPORTED\_ARRAY\_INT}{wxdefinesortedarray}\\

\membersection{Constructors and destructors}\label{arrayconstructorsdestructors}

Array classes are 100\% C++ objects and as such they have the appropriate copy
constructors and assignment operators. Copying wxArray just copies the elements
but copying wxObjArray copies the arrays items. However, for memory-efficiency
sake, neither of these classes has virtual destructor. It is not very important
for wxArray which has trivial destructor anyhow, but it does mean that you
should avoid deleting wxObjArray through a wxBaseArray pointer (as you would
never use wxBaseArray anyhow it shouldn't be a problem) and that you should not
derive your own classes from the array classes.

\helpref{wxArray default constructor}{wxarrayctordef}\\
\helpref{wxArray copy constructors and assignment operators}{wxarrayctorcopy}\\
\helpref{\destruct{wxArray}}{wxarraydtor}

\membersection{Memory management}\label{wxarraymemorymanagement}

Automatic array memory management is quite trivial: the array starts by
preallocating some minimal amount of memory (defined by
WX\_ARRAY\_DEFAULT\_INITIAL\_SIZE) and when further new items exhaust already
allocated memory it reallocates it adding 50\% of the currently allocated
amount, but no more than some maximal number which is defined by
ARRAY\_MAXSIZE\_INCREMENT constant. Of course, this may lead to some memory
being wasted (ARRAY\_MAXSIZE\_INCREMENT in the worst case, i.e. 4Kb in the
current implementation), so the \helpref{Shrink()}{wxarrayshrink} function is
provided to deallocate the extra memory. The \helpref{Alloc()}{wxarrayalloc}
function can also be quite useful if you know in advance how many items you are
going to put in the array and will prevent the array code from reallocating the
memory more times than needed.

\helpref{Alloc}{wxarrayalloc}\\
\helpref{Shrink}{wxarrayshrink}

\membersection{Number of elements and simple item access}\label{arrayelementsaccess}

Functions in this section return the total number of array elements and allow to
retrieve them - possibly using just the C array indexing $[]$ operator which
does exactly the same as \helpref{Item()}{wxarrayitem} method.

\helpref{Count}{wxarraycount}\\
\helpref{GetCount}{wxarraygetcount}\\
\helpref{IsEmpty}{wxarrayisempty}\\
\helpref{Item}{wxarrayitem}\\
\helpref{Last}{wxarraylast}

\membersection{Adding items}\label{arrayadding}

\helpref{Add}{wxarrayadd}\\
\helpref{Insert}{wxarrayinsert}\\
\helpref{SetCount}{wxarraysetcount}\\
\helpref{WX\_APPEND\_ARRAY}{wxappendarray}

\membersection{Removing items}\label{arrayremoving}

\helpref{WX\_CLEAR\_ARRAY}{wxcleararray}\\
\helpref{Empty}{wxarrayempty}\\
\helpref{Clear}{wxarrayclear}\\
\helpref{RemoveAt}{wxarrayremoveat}\\
\helpref{Remove}{wxarrayremove}

\membersection{Searching and sorting}\label{arraysearchingandsorting}

\helpref{Index}{wxarrayindex}\\
\helpref{Sort}{wxarraysort}

%%%%% MEMBERS HERE %%%%%
\helponly{\insertatlevel{2}{

\wxheading{Members}

}}

\membersection{WX\_DEFINE\_ARRAY}\label{wxdefinearray}

\func{}{WX\_DEFINE\_ARRAY}{\param{}{T}, \param{}{name}}

\func{}{WX\_DEFINE\_EXPORTED\_ARRAY}{\param{}{T}, \param{}{name}}

\func{}{WX\_DEFINE\_USER\_EXPORTED\_ARRAY}{\param{}{T}, \param{}{name}, \param{}{exportspec}}

This macro defines a new array class named {\it name} and containing the
elements of type {\it T}. The second form is used when compiling wxWidgets as
a DLL under Windows and array needs to be visible outside the DLL.  The third is
needed for exporting an array from a user DLL.

Example:

\begin{verbatim}
WX_DEFINE_ARRAY_INT(int, MyArrayInt);

class MyClass;
WX_DEFINE_ARRAY(MyClass *, ArrayOfMyClass);
\end{verbatim}

Note that wxWidgets predefines the following standard array classes: wxArrayInt,
wxArrayLong and wxArrayPtrVoid.

\membersection{WX\_DEFINE\_SORTED\_ARRAY}\label{wxdefinesortedarray}

\func{}{WX\_DEFINE\_SORTED\_ARRAY}{\param{}{T}, \param{}{name}}

\func{}{WX\_DEFINE\_SORTED\_EXPORTED\_ARRAY}{\param{}{T}, \param{}{name}}

\func{}{WX\_DEFINE\_SORTED\_USER\_EXPORTED\_ARRAY}{\param{}{T}, \param{}{name}}

This macro defines a new sorted array class named {\it name} and containing
the elements of type {\it T}. The second form is used when compiling wxWidgets as
a DLL under Windows and array needs to be visible outside the DLL.  The third is
needed for exporting an array from a user DLL.

Example:

\begin{verbatim}
WX_DEFINE_SORTED_ARRAY_INT(int, MySortedArrayInt);

class MyClass;
WX_DEFINE_SORTED_ARRAY(MyClass *, ArrayOfMyClass);
\end{verbatim}

You will have to initialize the objects of this class by passing a comparison
function to the array object constructor like this:

\begin{verbatim}
int CompareInts(int n1, int n2)
{
    return n1 - n2;
}

wxSortedArrayInt sorted(CompareInts);

int CompareMyClassObjects(MyClass *item1, MyClass *item2)
{
    // sort the items by their address...
    return Stricmp(item1->GetAddress(), item2->GetAddress());
}

wxArrayOfMyClass another(CompareMyClassObjects);
\end{verbatim}