Pointers

Dynamic Memory Management

• It means run time memory management i.e. while our program is being executed we can run time reserve memory according to our requirement, use it & release it after its use.
• To perform this type of operations c language provides us different library functions.
• These functions are declared in header file /

malloc()

• It dynamically reserves a block of memory.
• malloc reserves a block of size bytes dynamically.
• On success, malloc returns starting address of the newly allocated block of memory.
• On error (if not enough space exists for the new block), malloc returns a special value NULL.

        int*p;
        -----
        p = malloc(500);

calloc ()

• This function is used to reserve multiple blocks of fixed size.
• calloc allocates n consecutive blocks of specified bytes and initialize it to 0
• On success, returns starting address of first block.
• On failure (not enough space exists for the new block), returns NULL.

        int*p;
        -----
        p=calloc(4,100);

realloc()

• It reallocates a previously allocated block.
• realloc adjusts the size of the allocated block to newsize, copying the contents to a new location if necessary.
• On success, realloc returns a pointer to the newly allocated block of memory.
• On error (if not enough space exists for the new block), realloc returns NULL.

        int *p;
        p = malloc(200);
        p = realloc( p , 500);

free ()

• It releases the memory block which was dynamically reserved.
• It releases the memory block pointed by specified pointer.

        int*p;
        p = malloc(500);
        free( p );

  #include<stdio.h>
  main()
  {
    int i,n,s,*p ;
    printf("how many nos ");
    scanf("%d",&n);
    p=malloc(n*4);
    printf("enter %d nos.",n);
    for(i=0;i<n;i++)
        scanf("%d",p+i);
    s=0;
    for(i=0;i<n;i++)
        s=s+*(p+i);
    printf("sum is %d",s);
    free(p);
  }

How many nos 5
5 7 6 1 2
Sum is 21