Skip to main content

Dynamic allocation

Dynamic allocation
Dynamic allocation


Why And How 

In many situations the programmer does not know when he writes a program
what objects he will need. It can be that he does not know if he will need a
given object, or or that he does not know the size of a required array.
The new operator allows to create an object at run-time. This operator takes
as an operand a type, which may be followed either by a number of elements
between [ ] or by an initial value between ( ) :

char *c = new char;
int *n = new int(123);
double *x = new double[250];

The area of memory allocated by new is still used out of the pointer’s
scope!

Bugs due to missing object deallocation are called memory leaks.
To free the memory, the programmer has to explicitly indicate to the computer
to do so. The delete operator (resp. delete[]) takes a pointer to a single
object (resp. an array of objects) as an operand and free the corresponding
area of the memory ;

delete n;
delete[] x;

The variables declared in the source code, without the usage of new and delete
are called static variables. Their existence is completely handled by the com-
piler who implicitly adds invisible news and deletes.

The operand pointer can be equal to 0 ; in that case delete (or delete[]) does
nothing. But deallocating an area which has already been deallocated has a
non-defined behavior (i.e. crashes most of the time).
Labels:

Popular posts from this blog

C++ Program to find the sum, difference, product and quotient of two integers

#include <iostream.h> #include <conio.h> void main() {   clrscr();   int x = 10;   int y = 2;   int sum, difference, product, quotient;   sum = x + y;   difference = x - y;   product = x * y;   quotient = x / y;   cout << "The sum of " << x << " & " << y << " is " << sum << "." << endl;   cout << "The difference of " << x << " & " << "y <<  is " << difference << "." << endl;   cout << "The product of " << x << " & " << y << " is " << product << "." << endl;   cout << "The quotient of " << x << " & " << y << " is " << quotient << "." << endl;   getch(); }
Read more

Program of virtual piano

//////////////Tested And Created By C++/////////////////////////////// #include<stdio.h> #include<dos.h> #include<conio.h> #include<stdlib.h> #define SHOW 1 #define HIDE 2 union REGS input,output; class piano {  public:int BIGKEY,MIDKEY,back,border;     piano()//init constructor     {         BIGKEY=15;         MIDKEY=1;         back=7;         border=15;     } }color; void drawpiano(int x,int y); int check_xy(int x,int y); void BOX(int c,int r,int c1,int r1,int col); int initmouse(); void setupscreen(); void pointer(int on); void restrictmouse(int x1,int y1,int x2,int y2); void check_keys(int x,int y); void getmouse(int *button,int *x,int *y); float freq[7] = {130.81, 146.83, 164.81, 174.61,196, 220, 246.94 } ; int n=0,a=4,backcolor=2,exitcode=1; void showbar(int t) {  if(t>65) t=65;  if(t<1) t=1;  textcolor(15);  for(int q=0;q<=t;t++)  {     gotoxy(3+q,4);     cprintf("Û");  } } void main() {  int
Read more

Putimage function in c

putimage function outputs a bit image onto the screen. Declaration:- void putimage(int left, int top, void *ptr, int op); putimage puts the bit image previously saved with getimage back onto the screen, with the upper left corner of the image placed at (left, top). ptr points to the area in memory where the source image is stored. The op argument specifies a operator that controls how the color for each destination pixel on screen is computed, based on pixel already on screen and the corresponding source pixel in memory. c smiling face animation This animation using c draws a smiling face which appears at random position on screen. See output below the code, it will help you in understanding the code easily. C programming code #include<graphics.h> #include<conio.h> #include<stdlib.h>   main() { int gd = DETECT, gm, area, temp1, temp2, left = 25, top = 75; void *p;   initgraph(&gd,&gm,"C:\\TC\\BGI");   setcolor(YELLOW);
Read more