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Main Index

Chapter 5 – Pointers and Dynamic Memory. 1. Main Index. Contents. Pointer Illustration Vertical / Horizontal View . . . Data Addresses in Memory Declaring Pointer Variables Assigning Values to Pointers Accessing Data with Pointers Arrays and Pointers Operator ‘new’ Operator ‘delete’

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Main Index

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  1. Chapter 5 – Pointers and Dynamic Memory 1 Main Index Contents • Pointer Illustration • Vertical / Horizontal View . . . • Data Addresses in Memory • Declaring Pointer Variables • Assigning Values to Pointers • Accessing Data with Pointers • Arrays and Pointers • Operator ‘new’ • Operator ‘delete’ • Illustrating the Destructor • Copy Constructor / Overloaded Assignment Operator • Declaration of dynamicClass Objects • The Pointer ‘this’ • dynamicClass Copy Constructor • The C++ Index Operator [] • Matrices • Summary Slides (3 pages)

  2. 2 Main Index Contents Pointer Illustration

  3. 3 Main Index Contents Vertical and Horizontal View of Memory

  4. 4 Main Index Contents Data Addresses in Memory

  5. type *ptr; int *intPtr; char *charPtr; 5 Main Index Contents Declaring Pointer Variables • Declare a pointer by stating the type followed by the variable name, but with a "*" added immediately before the name. • The pointer ptr is a variable whose value is the address of a data item of the designated type.

  6. Assigning Values to Pointers • &m is the address of the integer in memory. The assignment statement • sets intPtr to point at an actual data item. • The Figure illustrates the status of the two variables from the declaration statement and the resulting status after the assignment of a value to intPtr. int m = 50, *intPtr; intPtr = &m;

  7. 7 Main Index Contents Accessing Data with Pointers int x = 50, y = 100, *px = &x, *py = &y;

  8. 8 Main Index Contents Arrays and Pointers

  9. 9 Main Index Contents Operator ‘new’ p = new time24; // *p is 00:00 (midnight) q = new time24(8, 15); // *q is 8:15 AM

  10. Operator ‘delete’ • deallocating a dynamic array, use a slightly different form of delete. Place square brackets [] between delete and the pointer variable name. The system deallocates all of the memory originally assigned to the dynamic array. arr = new T[ARRSIZE]; // allocated space for ARRSIZE objects delete [] arr; // deallocate dynamic array storage

  11. 11 Main Index Contents Illustrating the Destructor

  12. Copy Constructor / Overloaded Assignment Operator InitializationandAssignment both have the effect of producing a data item that is a copy of an existing item

  13. 13 Main Index Contents Declaration of dynamicClass Objects • The byte-by-bytecopy performed by default by C++ is inappropriate for dynamic classes • The copy of an objA in ObjB makes two pointers point at the same memory location. • This creates a memory leak when one of the two objects is deleted.

  14. IS the object *this objA; this-> memberl Points to the Object The Pointer ‘this’

  15. 15 Main Index Contents dynamicClass Copy Constructor Algorithm Example: dynamicClass<int> obj(3,5), objB=objA;

  16. The MiniVector • Check the code of the MiniVector • A small version of the Vector Class available in STL • The MiniVector uses a function called Reserve() to allocate a dynamic array for extra space

  17. The C++ Index Operator [ ] arr[i] = 30; // arr[i] is the address into which 30 is copied t = arr[i] + 4; // add 4 to the value of the element at arr[i]

  18. 18 Main Index Contents Matrices • A Matrix is a two-dimensional array that corresponds to a row-column table of entries of a specified data type. • Matrices are referenced using a pair of indices that specify the row and column location in the table. Example: The element mat[0][3] is 2 The element mat[1][2] is 4.

  19. 19 Main Index Contents Vectors and Matrices • A dynamic Matrix is represented by using the Vector Class. • Visit the matrix.h file • A dynamic Matrix can be described by using dynamic arrays as well. The code is more complex than using vectors. ( Think!) - Food for you brain • How would you define a dynamic matrix by using a dynamic array?

  20. 20 Main Index Contents Summary Slide 1 §- Pointerscontain the address of data in memory… - Data is accessed by applying the dereference operator * §- Operators such as +, ++, and += apply to pointers. §- With such operators, pointers can be used for algorithms involving array traversal, but their primary application is in the allocation and maintenance of dynamic memory.

  21. 21 Main Index Contents Summary Slide 2 §- vector implementation - The miniVector class illustrates the key points. 1) It allocates dynamic memory using: destructor copy constructor overloaded assignment operator 2) It implements push_back(): Therefore it must control vector capacity in order to minimize dynamic memory reallocation. 3) It allows access to elements by using an index: Therefore the class implements an overloaded index operator

  22. 22 Main Index Contents Summary Slide 3 §- Two dimensional arrays in C++ - have the same problems as one-dimensional arrays: 1) fixed size 2) no size attribute 3) If it is a function argument, it is necessary to specify the number of columns as a constant.

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