Differences

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--- qt:heap_versus_stack [2010/12/08 22:11] – [Heap or Stack?] mithat
+++ qt:heap_versus_stack [2010/12/08 22:59] (current) – mithat
@@ Line 1: / Line 1: @@
 ====== Heap or Stack? ======
-Should Qt objects be created on the heap or on the stack?((Reminder: the heap is the memory store from which dynamically allocated storage is taken; the stack is used for standard variable storage as well as for passing values to functions, etc.))
+Should Qt objects be created on the heap or on the stack?((Reminder: the heap is the memory store from which dynamically allocated storage is taken; the stack is used for standard variable storage as well as for passing actual parameters to functions, etc.))
 ===== Short answer =====
 If the object is going to be part of a tree of Qt objects (as will be the case for most Qt GUI objects), then it should be created on the heap.
-If the object is not part of a tree or is the root of a tree, then it can be created either on the heap or the stack. It seems to be a tradition (or maybe there's a good technical reason for this) to create the main QApplication on the stack.
+If the object is not part of a tree or is the root of a tree, then it can be created either on the heap or the stack. It seems to be a tradition (or maybe there's a good technical reason for this) to create the main ''QApplication'' object on the stack. It is also typical to create main windows (tree roots) on the stack so that they do not need to be manually deleted.
 ===== Long answer =====
@@ Line 14: / Line 14: @@
 For this to work, there are two requirements:
-  - All child objects must be created on the heap; however, the root itself may be on the stack. In other words, child objects that you intend to place in the tree must be created dynamically (using ''new'').
+  - All child objects must be created on the heap; however, the root itself may be on the stack. In other words, child objects that you intend to place in the tree must be created dynamically using the ''new'' operator.
   - Child objects must explicitly be made children of their parents (i.e., they must be //reparented//). Constructors for (re)parentable Qt objects let you pass parameters to specify the parent.
@@ Line 20: / Line 20: @@
 <code cpp-qt>
 QObjectSubclass theParent;                              // create theParent on the stack
+AnotherQObjectSubclass *foo;                            // pointer to a child
-AnotherQObjectSubclass *foo;
+foo = new AnotherQObjectSubclass( "bar", &theParent );  // create foo on the heap and reparent to theParent
-foo = new AnotherQObjectSubclass( "foo", &theParent );  // create foo on the heap and reparent to theParent
 </code>
 ===== Automatic Management with Layout Managers =====
-When widgets are added to [[layout managers]], they are automatically reparented to FIXME (the layout manager's parent)|(the layout manager). Therefore, parents are not specified when creating widgets that are added to layout managers. However, you must reparent the layout manager.
+When widgets are added to [[layout managers]], they are automatically reparented to the overlying object (typically the layout manager's parent). Therefore, parents are not specified when creating widgets that are added to layout managers. However, you must reparent the layout manager itself.
 <code cpp-qt>