CISC181 Introduction to Computer Science Dr. McCoy Lecture 18 October 29, 2009Pointer AssignmentsPointer Assignments Graphic: Display 10.1 Uses of the Assignment Operator with Pointer VariablesThe new OperatorBasic Pointer Manipulations Example: Display 10.2 Basic Pointer Manipulations (1 of 2)Basic Pointer Manipulations Example: Display 10.2 Basic Pointer Manipulations (2 of 2)Basic Pointer Manipulations Graphic: Display 10.3 Explanation of Display 10.2More on new OperatorPointers and FunctionsMemory ManagementChecking new Successnew Success – New CompilerFreestore Sizedelete OperatorDangling PointersDynamic ArraysArray VariablesArray Variables  PointersSlide 19Slide 20Creating Dynamic ArraysDeleting Dynamic ArraysFunction that Returns an ArrayDestructor NeedDestructorsCopy ConstructorsSummary 1Summary 2Go over Homework6.5 Implementing a Time Abstract Data Type with a class6.6 Class Scope and Accessing Class MembersSlide 326.6 Class Scope and Accessing Class Membersfig06_04.cpp (1 of 2)fig06_04.cpp (2 of 2) fig06_04.cpp output (1 of 1)Another Example6.7 Separating Interface from Implementation6.7 Separating Interface from Implementationtime1.h (1 of 1)time1.cpp (1 of 3)time1.cpp (2 of 3)time1.cpp (3 of 3)fig06_07.cpp (1 of 2)fig06_07.cpp (2 of 2) fig06_07.cpp output (1 of 1)6.8 Controlling Access to Membersfig06_08.cpp (1 of 1)fig06_08.cpp output (1 of 1)6.8 Controlling Access to Members6.9 Access Functions and Utility Functionssalesp.h (1 of 1)salesp.cpp (1 of 3)salesp.cpp (2 of 3)salesp.cpp (3 of 3)fig06_11.cpp (1 of 1)fig06_11.cpp output (1 of 1)6.10 Initializing Class Objects: Constructors6.11 Using Default Arguments with Constructorstime2.h (1 of 1)time2.cpp (1 of 3)time2.cpp (2 of 3)time2.cpp (3 of 3)fig06_14.cpp (1 of 2)fig06_14.cpp (2 of 2)fig06_14.cpp output (1 of 1)6.12 Destructors6.14 Using Set and Get Functionstime3.h (1 of 2)time3.h (2 of 2)time3.cpp (1 of 4)time3.cpp (2 of 4)time3.cpp (3 of 4)time3.cpp (4 of 4)fig06_20.cpp (1 of 3)fig06_20.cpp (2 of 3)fig06_20.cpp (3 of 3)fig06_20.cpp output (1 of 1)1CISC181 Introduction to Computer ScienceDr. McCoyLecture 18October 29, 2009Pointer Assignments•Pointer variables can be "assigned":int *p1, *p2;p2 = p1;–Assigns one pointer to another–"Make p2 point to where p1 points"•Do not confuse with:*p1 = *p2;–Assigns "value pointed to" by p1, to "valuepointed to" by p210-2Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Pointer Assignments Graphic: Display 10.1 Uses of the Assignment Operator with Pointer Variables10-3Copyright © 2010 Pearson Addison-Wesley. All rights reserved.The new Operator•Since pointers can refer to variables…–No "real" need to have a standard identifier•Can dynamically allocate variables–Operator new creates variables•No identifiers to refer to them•Just a pointer!•p1 = new int;–Creates new "nameless" variable, andassigns p1 to "point to" it–Can access with *p1•Use just like ordinary variable10-4Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Basic Pointer Manipulations Example: Display 10.2 Basic Pointer Manipulations (1 of 2)10-5Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Basic Pointer Manipulations Example: Display 10.2 Basic Pointer Manipulations (2 of 2)10-6Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Basic Pointer Manipulations Graphic: Display 10.3 Explanation of Display 10.210-7Copyright © 2010 Pearson Addison-Wesley. All rights reserved.More on new Operator•Creates new dynamic variable•Returns pointer to the new variable•If type is class type:–Constructor is called for new object–Can invoke different constructor withinitializer arguments:MyClass *mcPtr;mcPtr = new MyClass(32.0, 17);•Can still initialize non-class types:int *n;n = new int(17); //Initializes *n to 1710-8Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Pointers and Functions•Pointers are full-fledged types–Can be used just like other types•Can be function parameters•Can be returned from functions•Example:int* findOtherPointer(int* p);–This function declaration:•Has "pointer to an int" parameter•Returns "pointer to an int" variable10-9Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Memory Management•Heap–Also called "freestore"–Reserved for dynamically-allocated variables–All new dynamic variables consume memoryin freestore•If too many  could use all freestore memory•Future "new" operations will fail if freestoreis "full"10-10Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Checking new Success•Older compilers:–Test if null returned by call to new:int *p;p = new int;if (p == NULL){ cout << "Error: Insufficient memory.\n"; exit(1);}–If new succeeded, program continues10-11Copyright © 2010 Pearson Addison-Wesley. All rights reserved.new Success – New Compiler•Newer compilers:–If new operation fails:•Program terminates automatically•Produces error message•Still good practice to use NULL check10-12Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Freestore Size•Varies with implementations•Typically large–Most programs won’t use all memory•Memory management–Still good practice–Solid software engineering principle–Memory IS finite•Regardless of how much there is!10-13Copyright © 2010 Pearson Addison-Wesley. All rights reserved.delete Operator•De-allocate dynamic memory–When no longer needed–Returns memory to freestore–Example:int *p;p = new int(5);… //Some processing…delete p;–De-allocates dynamic memory "pointed to bypointer p"•Literally "destroys" memory10-14Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Dangling Pointers•delete p;–Destroys dynamic memory–But p still points there!•Called "dangling pointer"–If p is then dereferenced ( *p )•Unpredicatable results!•Often disastrous!•Avoid dangling pointers–Assign pointer to NULL after delete:delete p;p = NULL;10-15Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Dynamic Arrays•Array variables–Really pointer variables!•Standard array–Fixed size•Dynamic array–Size not specified at programming time–Determined while program running10-16Copyright © 2010 Pearson Addison-Wesley. All rights reserved.Array Variables•Recall: arrays stored in memoryaddresses, sequentially–Array variable "refers to" first indexed variable–So array variable is a kind of pointer