docs/doxygen/overviews/container.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        container.h
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows licence
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10
  11 @page overview_container Container Classes
  12
  13 @tableofcontents
  14
  15 For historical reasons, wxWidgets uses custom container classes internally.
  16 This was unfortunately unavoidable during a long time when the standard library
  17 wasn't widely available and can't be easily changed even now that it is for
  18 compatibility reasons. If you are building your own version of the library and
  19 don't care about compatibility nor slight (less than 5%) size penalty imposed
  20 by the use of STL classes, you may choose to use the "STL" build of wxWidgets
  21 in which these custom classes are replaced with their standard counterparts and
  22 only read the section @ref overview_container_std explaining how to do it.
  23
  24 Otherwise you will need to know about the custom wxWidgets container classes
  25 such as wxList<T> and wxArray<T> if only to use wxWidgets functions that work
  26 with them, e.g. wxWindow::GetChildren(), and you should find the information
  27 about using these classes below useful.
  28
  29 Notice that we recommend that you use standard classes directly in your own
  30 code instead of the container classes provided by wxWidgets in any case as the
  31 standard classes are easier to use and may also be safer because of extra
  32 run-time checks they may perform as well as more efficient.
  33
  34 Finally notice that recent versions of wxWidgets also provide standard-like
  35 classes such as wxVector<T>, wxStack<T> or wxDList which can be used exactly
  36 like the std::vector<T>, std::stack<T> and std::list<T*>, respectively, and
  37 actually are just typedefs for the corresponding types if wxWidgets is compiled
  38 in STL mode. These classes could be useful if you wish to avoid the use of the
  39 standard library in your code for some reason.
  40
  41 To summarize, you should use the standard container classes such as
  42 std::vector<T> and std::list<T> if possible and wxVector<T> or wxDList<T> if
  43 it isn't and only use legacy wxWidgets containers such as wxArray<T> and
  44 wxList<T> when you must, i.e. when you use a wxWidgets function taking or
  45 returning a container of such type.
  46
  47 @see @ref group_class_containers
  48
  49
  50
  51 @section overview_container_legacy Legacy Classes
  52
  53 The list classes in wxWidgets are doubly-linked lists which may either own the
  54 objects they contain (meaning that the list deletes the object when it is
  55 removed from the list or the list itself is destroyed) or just store the
  56 pointers depending on whether or not you called wxList<T>::DeleteContents()
  57 method.
  58
  59 Dynamic arrays resemble C arrays but with two important differences: they
  60 provide run-time range checking in debug builds and they automatically expand
  61 the allocated memory when there is no more space for new items. They come in
  62 two sorts: the "plain" arrays which store either built-in types such as "char",
  63 "int" or "bool" or the pointers to arbitrary objects, or "object arrays" which
  64 own the object pointers to which they store.
  65
  66 For the same portability reasons, the container classes implementation in
  67 wxWidgets don't use templates, but are rather based on C preprocessor i.e. are
  68 implemented using the macros: WX_DECLARE_LIST() and WX_DEFINE_LIST() for the
  69 linked lists and WX_DECLARE_ARRAY(), WX_DECLARE_OBJARRAY() and
  70 WX_DEFINE_OBJARRAY() for the dynamic arrays.
  71
  72 The "DECLARE" macro declares a new container class containing the elements of
  73 given type and is needed for all three types of container classes: lists,
  74 arrays and objarrays. The "DEFINE" classes must be inserted in your program in
  75 a place where the @e full declaration of container element class is in scope
  76 (i.e. not just forward declaration), otherwise destructors of the container
  77 elements will not be called!
  78
  79 As array classes never delete the items they contain anyhow, there is no
  80 WX_DEFINE_ARRAY() macro for them.
  81
  82 Examples of usage of these macros may be found in wxList<T> and wxArray<T>
  83 documentation.
  84
  85 Finally, wxWidgets predefines several commonly used container classes. wxList
  86 is defined for compatibility with previous versions as a list containing
  87 wxObjects and wxStringList as a list of C-style strings (char *), both of these
  88 classes are deprecated and should not be used in new programs. The following
  89 array classes are defined: wxArrayInt, wxArrayLong, wxArrayPtrVoid and
  90 wxArrayString. The first three store elements of corresponding types, but
  91 wxArrayString is somewhat special: it is an optimized version of wxArray which
  92 uses its knowledge about wxString reference counting schema.
  93
  94
  95
  96 @section overview_container_std STL Build
  97
  98 To build wxWidgets with the standard containers you need to set
  99 wxUSE_STD_CONTAINERS option to 1 in @c wx/msw/setup.h for wxMSW builds or
 100 specify @c --enable-std_containers option to configure (which is also
 101 implicitly enabled by @c --enable-stl option) in Unix builds.
 102
 103 The standard container build is mostly, but not quite, compatible with the
 104 default one. Here are the most important differences:
 105  - wxList::compatibility_iterator must be used instead of wxList::Node* when
 106    iterating over the list contents. The compatibility_iterator class has the
 107    same semantics as a Node pointer but it is an object and not a pointer, so
 108    you need to write
 109         @code
 110         for ( wxWindowList::compatibility_iterator it = list.GetFirst();
 111               it;
 112               it = it->GetNext() )
 113             ...
 114         @endcode
 115    instead of the old
 116         @code
 117         for ( wxWindowList::Node *n = list.GetFirst(); n; n = n->GetNext() )
 118             ...
 119         @endcode
 120  - wxSortedArrayString and wxArrayString are separate classes now and the
 121    former doesn't derive from the latter. If you need to convert a sorted array
 122    to a normal one, you must copy all the elements. Alternatively, you may
 123    avoid the use of wxSortedArrayString by using a normal array and calling its
 124    Sort() method when needed.
 125  - WX_DEFINE_ARRAY_INT(bool) cannot be used because of the differences in
 126    std::vector<bool> specialization compared with the generic std::vector<>
 127    class. Please either use std::vector<bool> directly or use an integer array
 128    instead.
 129
 130 */