The a u t o - g t r wraps a its destructor calls in Java

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The a u t o - g t r wraps a its destructor calls
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The recently adopted C++ standard contains a new wrapper class called the auto-gtr, which helps automatically delete dynamically allocated objects This class is intended to help solve three common C++ pointer problems Recall that, if an ob-jectis dynamically allocated by a call to new,it must eventually be freed by a call to deleteOtherwise, we can have a memory (or other resource) leak The autostr helps do this task automatically by
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wrapping the pointer inside the auto-ptr class and then having the auto-ptr destructor call deleteThe auto-ptr class is designed for three scenarios In the first scenario, inside a function a local pointer variable allocates, via new,an object that has local scope only When the function returns, the object is expected to be freed by a call to deleteTypical code looks like:
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void func i
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scenario I: We need a local dynamically allocated object
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Object *obj
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new Object(
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delete obj;
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This code seems simple enough, but some dangers are lurking If func has multiple returns, we must ensure that delete is always reached And if func throws an uncaught exception, the delete never occurs However, as destructors are always called when a function exits (even if via an uncaught exception), if the pointer is wrapped inside an ob-ject whose destructor calls delete,the memory will be reclaimed The second scenario is a function that allocates an object and returns a pointer to it The caller is now expected to call delete when it no longer needs the object Typical code looks like:
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scenario 2: We need an Object created and returned from a completed function call
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Object *funcl( ) i Object *objl
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new Object( 1 ;
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return objl;
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void func( ) i Object *obj
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funcl( i
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delete obj;
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This scenario has problems similar to those of the first scenario (we must be sure to reach the delete in all cases) except that we must ensure that delete is not called in f uncl
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Scenario 3: We need to delete a dynamically allocated object created by the calling function
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A third scenario is a function that allocates an object and then calls another function, with the expectation that the other function will clean up,
void f u n c ( Object *obj )
delete obj;
void f u n c l ( ) O b j e c t * o b j l = new O b j e c t (
Do not use
auto-ptr for more
than intended by its designers
The destructor calls delete if it owns the pointee
Here funcl creates an object, sends a pointer to it to func and expects func to eventually call delete These tasks are all that auto-ptr is expected to be used for Fancier automatic garbage collection requires more sophisticated logic The basic property of the auto-ptr wrapper is as follows It wraps the pointer variable (thus storing the value of the pointer as the pointee data member) It also indicates whether it is the owner of the pointer (as a Boolean isowner) If it is the owner, then when its destructor is called it must apply the delete operator to the pointer When a copy is performed, ownership is transferred Figure 59 illustrates our version, the AutoPointerThe basic constructor is shown starting at line 7 It simply sets pointee and isowner The destructor calls the private member function free,which itself calls delete if the AutoPointer is the owner (of pointee) Lines 37 and 38 implement some of the same logic used in the Pointer class earlier in this section The code in lines 33 to 36 implements the dereferencing operator (which is the equivalent of *pointee)and - > (which is the equivalent of
pointee)
The release method gives up ownership of the pointee
Only three other methods are left: release,the copy constructor, and operator=The release method (lines 39 and 40) gives up ownership, but otherwise behaves like getIt can be called when control is transferred by a copy operation Thus, in the copy constructor at lines LO and 1 1 , instead of copyi n g t h e p o i n t e r v a l u e w i t h p o i n t e e = r h s p o i n t e e ,we u s e rhs pointee release ( ) on the right-hand side rhs's ownership is