Memory Management and Dynamic Structures: Pointers, Dynamic Variables, and Arrays - Prof. , Study notes of Electrical and Electronics Engineering

Download Memory Management and Dynamic Structures: Pointers, Dynamic Variables, and Arrays - Prof. and more Study notes Electrical and Electronics Engineering in PDF only on Docsity! Pointers and Dynamic Structures  Overview of Memory Model  Pointer Variables  Using Dynamic Variables and Arrays  Using Dynamic Structures and Arrays of Structures  Reference Parameters Revisited  Class Constructors  Copy Constructors  Class Destructors Overview of Memory Model  Computer memory can be viewed as an "array" of storage locations  On a PC this array may be limited to size of physical memory  On a workstation "virtual" memory size is almost unlimited  Memory at run time typically contains the following: O/S Code O/S Data Program Code Program Data The Stack Free Memory The Heap 1 - operating system code  The O/S code is loaded into memory when machine "boots"  This code is executed when O/S functions are called 2 - operating system data  Provides space for all global variables of the O/S  On some systems this data may be on the stack 3 - program code  The program code is loaded when the program is "invoked"  The code is executed when program functions are called 4 - program data  Provides space for all global variables of the program  On some systems this data may be on the stack Using Dynamic Variables and Arrays  Pointers can also contain addresses of space requested from the heap  Must specify amount of space needed (number & types of variables)  Different data types are different sizes (char=1, int=4, float=4, etc.)  This mechanism gives us a way to create variable sized arrays  The new command creates space, the delete command releases space  Use *data or data[i] to access dynamic variables or arrays  Use delete or delete [] to return memory to the heap // Allocate a dynamic variable int *value = NULL; value = new int; // Using a dynamic variable *value = 13; delete value; int *john = new int; cout << *john; // Allocate a dynamic array int size; cout << "Enter size of array:"; cin >> size; float *data = new float[size]; // Use the dynamic array for (int i=0; i < size; i++) data[i] = i * 3.14159 / size; delete []data; Using Dynamic Structures and Arrays of Structures  Can also request space for one or more structures on the heap  This is used for creating linked lists, trees, and graphs  Must define structure and use new and delete as before  Need to use data->Part or (*data).Part to refer to subparts // Allocate a dynamic structure struct student { char Name[20] int Year; float GPA; }; student *temp = new student; student junk; junk.Year = 2006; // Using a dynamic structure strcpy(temp->Name, "Tom Jones"); temp->Year = 2006; temp->GPA = 3.0; // Allocate a dynamic array of structures int size; cout << "Enter size of array:"; cin >> size; student *data = new student[size]; // Initialize dynamic array of structures for (int i=0; i < size; i++) { strcpy(data[i].Name, ""); data[i].Year = 2006; data[i].GPA = 0.0; } cin >> size; Point *p = new Point[size]; for (int i=0; i<size; i++) { p[i].setX( rand() % 100 ); p[i].setY( rand() % 100 ); } // Use dynamic array of structures student *ptr = NULL; for (int i=0; i < size; i++) if (strcmp(data[i].Name, "John Smith") == 0) ptr = data[i]; if (ptr != NULL) ptr->GPA = 3.5; // Release memory Class Constructors  The constructor function is called when a class variable is declared  This function has the same name as the class itself  Constructor initializes private data members of the class  Dynamic size objects can be created using the new command // Array class definition class Array { public: Array(int size); // constructor Array(const & Array); // copy constructor ~Array(); // destructor void ReadArray(char filename[]); void ProcessArray(int param); void WriteArray(char filename[]); private: int Length; int *Data; }; // Constructor function Array::Array(const int size) { Length = size; Data = new int[Length]; } // Write array data to file void Array::WriteArray(char filename[]) { ofstream dout(filename); for (int i=0; i<Length; i++) dout << Data[i] << " "; dout << endl; dout.close(); } // Main program int main() { int size; cin >> size; Array a(size); a.ReadArray("infile.txt"); a.ProcessArray(42); a.WriteArray("outfile.txt"); // magic call to “a” destructor } Copy Constructors  The copy constructor is used to create copies of objects  It is also used when objects are passed by value into functions  Important to define when dynamic memory is allocated in constructor  Without a copy constructor, dynamic objects should be passed by reference (or you will have a “shallow copy, deep destroy” bug) // Copy constructor function. Array::Array(const Array & a) { // Allocate space and make copy Length = a.Length; Data = new int[Length]; for (int i = 0; i < Length; i++) Data[i] = a.Data[i]; } // Usage example Array a(100); a.ReadArray("infile.txt"); Array b(a);