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C++ Pointers Dynamic Memory Allocation Pointers within Classes

Copy Constructors Destructors

STL list class Iterators Ncurses I/O

The text-based GUI

CSE 30331CSE 30331Lecture 8 – Pointers, Lists & NcursesLecture 8 – Pointers, Lists & Ncurses

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Pointer Illustration

// x is an int and// ip points to an intint x, *ip; x = 37; ip = &x; the data

// fp points to a// dynamically allocated and // nameless float float *fp; the pointer fp = new float;*fp = -87.5;

A d d res s

D at a co n t en t s

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Data Addresses in Memory

50

in t eger ch ar

5 0 0 0

S

5 0 0 4 5 0 0 5

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Pointer declaration format

<type> * <ptr_name>;

The declared pointer is a variable whose value is the address of a data item of the designated type.

int *intPtr;

char *charPtr;

Declaring Pointer Variables

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int m = 50, *intPtr;

// here intPtr “points to” nothing

intPtr = &m; // &m is the address of m

// now intPtr “point to” m

Assigning Values to Pointers

5 0m

?in tP tr

?

5 0

m

& m

in tP tr(a) A fte r d e c laratio n (b ) A fte r as s ig n m e n t

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Arrays and Pointers

a rr

a rr[0 ] a rr[6 ]a rr[5 ]a rr[4 ]a rr[3 ]a rr[2 ]a rr[1 ]

a rr+ 7a rr+ 2a rr+ 1

6000 602860206016601260086004 6032

a rr+ 5

The amount the pointer is incremented is based on the sizeof() the base type of the array

Ex: arr+5 is really &arr[0] + 5*sizeof(element_type)

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Dynamic Memory

Pointer Variable whose value is the address of another data value

Heap System managed store of memory available to be allocated

and deallocated while program is running New

operator to dynamically allocate memory from the heap for program use

Delete operator to dynamically deallocate memory no longer

needed by program and return it to the heap

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“new” and “delete” operators Allocating & deallocating a single data location

int *p = new int; // allocates itdelete p; // deallocates it

Allocating & deallocating a dynamic array Note square brackets used with delete operator. These ensure

system deallocates ALL locations in array, not just the first one.

// allocate space for 300 intsint *arr = new int[300]; // deallocate all 300 int locationsdelete [] arr;

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Pointers and classes Use # 1

Dynamically allocate and de-allocate class objects Use # 2

Dynamically allocate and de-allocate storage used by class member variables

Why is this important? When execution exits a block within which an object is

declared, a destructor is called automatically. The default destructor takes care of returning memory to

the heap in usage # 1. In usage # 2 we must write our own destructor to return the

memory used by member variables, else it is lost to the program creating a memory leak.

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Illustrating the Destructor

m e m be r1= m 1

B e fo re de s tro ying o bj Af te r de s tro ying o bj

m e m be r2m e m be r1= m 1 m e m be r2

m 2 m 2

O n he ap

\\

R e m ains o n the he ap with no thingpo int ing at i t .

Dynamic class from Ford & Topp (member 1 is data -- member 2 is a pointer)

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The destructortemplate<typename T>class myVector // super simple vector class{public: // the constructor allocates the array myVector(int n=0) : dSize(n), data(NULL) { if (dSize > 0) data = new T(dSize); } // the destructor deallocates the array ~myVector() { if (data != NULL) delete [] data; }private: T *data; // the dynamically allocated array int dSize; // the size of the array};

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Assignment & Copy Constructor C++ provides for every class, default …

destructor, assignment operator copy constructor

All of these are “shallow” They only copy or deallocate member variables, NOT what they “point to”

For all classes that contain member variables that point to dynamically allocated memory, we must create our own destructor, assignment operator and copy constructor

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// object A has 10 data locations and B is a copy of A// (but BOTH point to the same dynamically allocated array)

myVector<int> A(10), B(A);

A B nSize data nSize data

dynamically allocated array (10 locations)

Shallow Copy

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Copy Constructor / Overloaded Assignment Operator

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30

y

(a ) In i ti a l i z a ti on : ti m e 24 y = x

15

30

x

0

0

y

(b) As s i gn m e n t: z = x

15

30

x

15

30

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Copy Constructors

The Copy Constructor is called whenever ….

1)objects are passed as value parameters

2) an object is returned as the function value

3) an object is created and initialized with another object of the same class

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Copy Constructor Example: expanded myVector class

Note: parameter MUST be a reference parameter, because the copy constructor itself is used in passing by value

template<typename T>myVector<T>::myVector(const myVector<T>& v): dSize(v.dSize){ data = new T[v.dSize]; // allocate space for(int i=0; i<dSize; i++) data[i] = v.data[i]; // copy values}

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The Pointer ‘this’

*this objA;

this->memberl

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Vectors vs. Lists Vector

Direct access to elements by index Dynamically resizable at end Push_back, pop_back, and [ ] are Θ(1) Insert, delete are Θ(n) because they require shifting of

elements (n/2 on average) List

Sequential access to all elements Resizable by addition anywhere in list Element access is Θ(n) requiring list traversal Insert & delete are Θ(1), once we have access to the

element

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Model of a list object with links to next and previous elements

fro nt b ac k

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The List ADT

The list API provides three constructors to declare a list object.

0 .00 .0 0 .00 .0 0 .00 .0 0 .00 .0(a) lis t< d o ub le> realL is t(8)

8 :3 08 :3 0 8 :3 08 :3 0 8 :3 0 8 :3 0(b ) lis t< tim e24> tim eLis t(6, 8:30)

ar ray

(c ) lis t< s tring> s trL is t(s trA rr, s trA rr+ 3)l is tve c to r

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CLASS list Constructors <list>

list();Create an empty list. This is the default constructor.

list(int n, const T&value = T());Create a list with n elements, each having a specified value. If the value argument is omitted, the elements

are filled with the default value for type T. Type T must have a default constructor, and the default value of type T is specified by the notation T().

list(T *first, T *last);Initialize the list, using the address range [first, last).

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CLASS list Operations <list>

T& back();Return the value of the item at the rear of the list. Precondition: The vector must contain at least one

element.

bool empty() const;Return true if the vector is empty, false otherwise.

T& front();Return the value of the item at the front of the list. Precondition: The vector must contain at least one

element.

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CLASS list Operations <list>

void push_back(const T& value);Add a value at the rear of the list. Postcondition: The list has a new element at the

rear, and its size increases by 1.

void pop_back();Remove the item at the rear of the list. Precondition: The list is not empty. Postcondition: The list has a new element at the rear

or is empty.

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CLASS list Operations <list>

void push_front(const T& value);Add a value at the front of the list. Postcondition: The list has a new element at the

front, and its size increases by 1.

void pop_front();Remove the item at the front of the list. Precondition: The list is not empty. Postcondition: The list has a new element at the front

or is empty.

int size() const;Return the number of elements in the vector.

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CLASS list Operations <list>

iterator begin();Returns an iterator that references the first position

(front) of the list. If the list is empty, the iterator value end() is returned.

const_iterator begin();Returns a const_iterator that points to the first position (front) of a constant list. If the list is empty, the

const_iterator value end() is returned.

iterator end();Returns an iterator that signifies a location immediately out of the range of actual elements. A program must

not dereference the value of end() with the * operator.

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CLASS list Operations <list>

iterator end();Returns an iterator that signifies a location immediately out of the range of actual elements. A program must

not dereference the value of end() with the * operator.

const_iterator end();Returns a const_iterator that signifies a location

immediately out of the range of actual elements in a constant list. A program must not dereference the value of end() with the * operator.

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CLASS list Operations <list>

void erase(iterator pos);Erase the element pointed to by pos.Precondition: The list is not empty.Postcondition: The list has one fewer element.

void erase(iterator first, iterator last);Erase all list elements within the iterator range [first,

last].Precondition: The list is not empty.Postcondition: The size of the list decreases by the

number of elements in the range.

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CLASS list Operations <list>

iterator insert(iterator pos, const T& value);Insert value before pos, and return an iterator pointing to the position of the new value in the list. The

operation does not affect any existing iterators.Postcondition: The list has a new element.

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CLASS list::iterator Operations <list>

*:Accesses the value of the item currently pointed to by the iterator.

*iter;*iter;

++: Moves the iterator to the next item in the list. iter++;iter++;

--: Moves the iterator to the previous item in the list.

iter--;iter--;

==: Takes two iterators as operands and returns true when they both point at the same item in the list.

iter1 == iter2iter1 == iter2

!=: Returns true when the two iterators do not point at the same item in the list.

iter1 != iter2iter1 != iter2

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Palindromes

Strings that read the same forwards and backwards

Spaces and punctuation are ignored

Approaches (using lists) 1 – Pop matching pairs of 1st & last chars 2 – Scan inward to middle, matching

corresponding outermost pairs

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Palindrome (pop matches)// Assume spaces & punctuation removed// by caller; all letters in lower casetemplate<typename T>bool isPal_1(const list<T>& alist) { list<T> copyList; copyList = alist; while (copyList.size() > 0) { if (copyList.front() != copyList.back()) return false; // mismatch, not a palindrome // pop matching pair copyList.pop_front(); copyList.pop_back(); } return true; // all pairs matched & popped}

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Palindrome (scan inward)// Assume spaces & punctuation removed// by caller; all letters in lower casetemplate<typename T>bool isPal_2(const list<T>& alist) { list<T>::iterator left, right; left = alist.begin(); right = alist.end(); right--; while (left != right) { if (*left != *right) return false; // mismatch, not a palindrome right--; // move right iter 1 posit left if (left == right) return true; // even length string, we’re done left++; // move left 1 posit right } return true; // all pairs matched & popped}

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SeqSearch(no binary search possible here)

// search values [*first,*last)- sequentially

template<typename T>List<T>::iterator seqSearch ( list<T>::iterator& first, list<T>::iterator& last, const T& target){ list<T>::iterator iter = first; while((iter != last) && (*iter != target)) iter++; return iter;}

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Inserting an element into a list

fro nt

Lis t o b je c t (a fte r)

fro nt re a r

Lis t o b je c t (b e fo re )

ne w E ltre a r

ite r

2 55937 2 9374

ite r4

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Removing an element from a list

fro nt

Lis t o b je c t (a fte r)

fro nt re a r

Lis t o b je c t (b e fo re )

re a rite r

2 5937 2 593

ite r? ?

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Ordered Lists

Values maintained in order by key Numerical Alphabetical Lexicographical

Insertion is a two step process Search for first list value (V) greater than or equal to the

new value Insertion of new value in front of list value (V)

Ordered List Examples Inserting Removing duplicates

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Inserting in Ordered Listtemplate<typename T>void insertOrder (list<T>& orderedList, const T& item){ list<T>::iterator curr = orderedList.begin(), stop = orderedList.end();

// find insertion spot, 1st value >= item while((curr != stop) && (*curr < item)) curr++;

// insert item ahead of *curr orderedList.insert(curr, item);}

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Removing Duplicates// assume list is ordered. This way we can jump curr// ahead as soon as we find *p != *currtemplate<typename T>void removeDups (list<T>& orderedList) { list<T>::iterator curr, p; curr = orderedList.begin(); while (curr != orderedList.end()) { p = curr; p++; while ((p != orderedList.end() && (*p == *curr)) // pass p, move p forward, and call erase orderedList.erase(p++); curr = p; }}

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Curses Library

Allows “text-based” GUI

Curses or Ncurses for Unix/Linux/AIX Defined in “curses.h” header file

PDCurses (Public Domain Curses) for Dos/Windows

Supports mouse, keypads, color, buffered & non-buffered input, and some simple graphics (lines, boxes, etc)

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Curses (Windows, etc)

Curses works by creating a window / screen / console data structure within which the program moves the cursor and performs output

A refresh() function updates the actual window / screen / console to reflect the logical one

See class web site for URLs of Curses resources / tutorials / examples/ etc.

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Curses Basics – Hello World!#include<curses.h>int main(){ // always do this first initscr(); // initialize curses

// these are optional cbreak(); // input keys immediately available noecho(); // stop echoing inputs nonl(); // faster cursor movement clear(); // clear the screen // move cursor to location and output message // upper left screen corner is 0,0 move(12,5); // move cursor to row 12, column 5 printw(“Hello World\n”); // instead of cout << ... refresh(); // make it visible to us getch(); // wait for a key to be hit

endwin(); // release window back to shell return 0;}

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CursesInitialization & Shutdown

Must use … initscr(); // first, to initialize curses endwin(); // last, to return screen to normal

Probably use … cbreak(); // enable direct keystroke access noecho(); // prevent echoing of input nonl(); // speeds cursor movement getmaxyx(stdscr,h,w); // get screen limits

Notes: stdscr is the default screen/window

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CursesMoving cursor & I/O

Cursor & position move(y,x); // move cursor to line y, char posit x

Upper left of screen is at position 0,0 getyx(y,x); // returns current cursor location

I/O printw(“%d %s”, num, str); // cout <<

Parameters are same as printf() Prints in window from current cursor location

scanw(“%f”,&realNum); // cin >> Parameters are same as scanf() Reads input stream as directed by format string

getch(); // reads single keystroke wgetch(stdscr); // reads single keystroke

From indicated window

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CursesMoving cursor & I/O

Combined movement and I/O mvprintw(y,x,“%d %s”, num, str);

Prints in window from cursor location y, x mvscanw(y,x,“%f”,&realNum);

Reads input stream as directed by format string

Making it visible refresh(); // updates console

Makes it match logical window data structure

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Curses Color Only supported on certain terminal types (xterm is good bet)

set term=xterm at unix prompt before running program Or run in separate xterm using ...

xterm -geometry 80x50 -e tttCM start_color(); // initializes color init_pair(num,fg_color,bg_color); Creates a COLOR_PAIR of foreground and background colors xterm has 8 colors and 64 color pairs, max attron(COLOR_PAIR(num));

makes color pair the output attribute until turned off attroff(COLOR_PAIR(num));

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Curses COLORS

COLOR_BLACK COLOR_RED COLOR_GREEN COLOR_YELLOW COLOR_BLUE COLOR_MAGENTA COLOR_CYAN COLOR_WHITE

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Curses Using Special Keys

To use function keys, arrows, etc. Initialize with keypad(stdscr,TRUE); Must be used before both special key input And before mouse event capture prevents immediate translation to ASCII

Get key with int key = getch();

Test key with keycodes KEY_DOWN, KEY_UP, KEY_LEFT, KEY_RIGHT KEY_HOME, KEY_BACKSPACE KEY_F(n) Function keys, for 0 <= n >= 63 KEY_DC Delete character KEY_IC Insert char or enter insert mode KEY_ENTER Enter or send

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Curses Mouse Support

Only in Ncurses (Linux & AIX) Initialize for capture of events with

mousemask(ALL_MOUSE_EVENTS,NULL); Specific masks (BUTTON1_CLICKED, ...)

Read mouse click with int key = getch(); or int key = wgetch(stdscr);

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Curses Mouse Events Processing event

Value read will equal KEY_MOUSE Use getmouse(&event) to recover event from event queue Use event.bstate to determine button state (which event) Use event.x and event.y to determine where mouse was clicked in

window

MEVENT event; // data type for mouse event

int key = getch();

if (key == KEY_MOUSE) // if it was the mouse if (getmouse(&event) == OK) { // get the event if (event.bstate & BUTTON1_CLICKED) { // so do something with // event.y; and event.x;

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Example Curses Programs(on class web site) hi.cpp

Simple curses “Hello World” program bigHi.cpp

Shows big “HI” on screen hw4_sample.cpp

Shows size of curses window, once open mvbox.cpp

Moving star shape: Uses keyboard (letter) inputs mvbox2.cpp

Moving star and box shapes: Uses keyboard (letter) inputs mvbox3.cpp

Like mvbox2.cpp but also uses arrow keys and mouse tttCM (executable only)

TicTacToe: Uses Color, mouse and keyboard inputs