#include <memory> in Java

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#include <memory>
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The definition of an auto_ptr object takes one of the following three general forms:
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auto_ptr< type_pointed_to > identifier( ptr_allocated_by_new ); auto_ptr< type_pointed_to > identifier( auto_ptr_of_same_type ); auto_ptr< type_pointed_to > identifier;
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type_pointed_to represents the type of the object created by the new expression Let's look at each of the definitions in turn In the most common case, we wish to directly initialize the auto_ptr object to the address of an object returned by a new expression We can do this as follows:
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auto_ptr< int > pi( new int( 1024 ) );
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pi is initialized with the address of the object created by the new expression This object is initialized to the value 1,024 We can check the value of the object referred to by the auto_ptr object in the same way that we would with an ordinary pointer:
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if ( *pi != 1024 ) // oops, something wrong else *pi *= 2;
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The object created by the new expression to which pi refers is deleted automatically when the lifetime of pi ends If pi is a local object, the object to which pi refers is deleted at the end of the block in which pi is defined If pi is a global object, the object to which pi refers is deleted at the end of the program What if we initialize the auto_ptr object to refer to an object of class type, such as the standard string type For example:
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auto_ptr< string > pstr_auto( new string( "Brontosaurus" ) );
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Suppose that we now wish to access a string operation With an ordinary string pointer, we'd do the following:
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string *pstr_type = new string( "Brontosaurus" ); if ( pstr_type->empty() ) // oops, something wrong
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How would we access the string operation empty() using an auto_ptr object We'd use exactly the same approach:
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auto_ptr< string > pstr_auto( new string( "Brontosaurus" ) ); if ( pstr_auto->empty() ) // oops, something wrong
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The primary motive behind the auto_ptr class template is to support the same syntax as the one used with ordinary pointer types but additionally to provide for automatic management of the deletion of the object to which an auto_ptr object refers Common sense might lead you to believe that this additional security comes at the cost of run-time efficiency, but this is not the case Because support for these operations is inline (they are expanded at the point of call by the compiler), use of an auto_ptr object is not significantly more expensive than the direct use of a pointer What happens in the following case, in which we initialize pstr_auto2 with the value of pstr_auto, an auto_ptr to an underlying string object
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// who is responsible for deleting the string auto_ptr< string > pstr_auto2( pstr_auto );
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Suppose we directly initialize one string pointer with another, as in
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string *pstr_type2( pstr_type );
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Both pointers hold the address of the string within the program free store, and we must be careful to apply delete to only one of the pointers The auto_ptr class template, on the contrary, supports the notion of ownership When we define pstr_auto, it recognizes its ownership of the string with which we initialize it and recognizes that it is responsible for deleting the string This is the responsibility that ownership confers upon an auto_ptr object The question is, What happens in terms of ownership when pstr_auto2 is initialized to point to the same object as pstr_auto We don't want both auto_ptr objects to own the same underlying object that gives rise to all the problems of multiple deletions that we wanted to prevent by using the auto_ptr type in the first place When one auto_ptr object is initialized with or assigned to a second auto_ptr object, the left-hand auto_ptr object being initialized or assigned to now holds the ownership for the underlying object on the free store The right-hand auto_ptr object relinquishes all responsibility In our example, then, it is pstr_auto2 now that deletes the string object, and not pstr_auto, and pstr_auto can no longer be used to refer to the string object Similar behavior happens with the assignment operator Given the following two auto_ptr objects
auto_ptr< int > p1( new int( 1024 ) ); auto_ptr< int > p2( new int( 2048 ) );
the assignment operator can be used as follows to copy one auto_ptr object to another:
p1 = p2;
Prior to the assignment, the object referred to by p1 is deleted After the assignment, p1 has ownership of the object of type int containing the value 2,048 p2 can no longer be used to refer to this object In the third form of auto_ptr definition, we create an auto_ptr object but do not initialize it with a pointer to an object on the free store For example:
// does not currently refer to an object auto_ptr< int > p_auto_int;
Because p_auto_int is not initialized to refer to an object, its internal pointer value is set to 0 This means that dereferencing it would result in the program having undefined behavior, as would happen if we directly dereferenced a pointer of value 0:
// oops: dereference of an auto_ptr pointing to no object if ( *p_auto_int != 1024 ) *p_auto_int = 1024;
With an ordinary pointer, one simply tests the pointer against 0 For example:
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