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Pointer overview

Discussion in 'C' started by Jaihind, Aug 26, 2006.

  1. Jaihind

    Jaihind New Member

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    Pointer
    Pointer is a declared like a variable, but it's not an ordinary variable, it's a fancy variable, that can store address of the another variable. Pointer is very much useful for allocating memory at run time , that's dynamic allocation. Pointers are said to "point to" the variable whose reference they store ( * - Dereference operator ).

    See the Following Declarations

    int *iA; // integer pointer
    char *szB; // character pointer
    float *fC; // floating pointer

    Here iA, szB and fC are pointer variables, the variables capable of holding addresses.

    Main features of pointer
    1. To Reduce the wastage of Memory
    2. Increase the Programming Speed
    3. Data manipulations (Linked list , Stack , Queue , trees.., )

    int a[]={10,20,30,40,50};
    int *ptr=&a[0];

    ptr contains base address of array ' a '
    base address points first element of an array 'a'

    Pointer Supports Dynamic Memory Management

    Windows "C "
    Code:
    int a[10];					
    int *p;						
    p= (int *)malloc(sizeof(a));                         
    free(p); 
    Code:
    int b[10][10]; 
    int **q;
    *q=(int *)malloc(sizeof(b));
    free(*p);
    Windows "C++"

    Code:
    int a[10];
    int *p=new int[sizeof(a)];
    delete []p;
    Code:
    int b[10][10];
    int **q;
    *q=new int[sizeof(b)];
    delete []*q;
    Using the above functions you can effectively manage ( allocate and deallocate ) memory.

    Function Pointers

    Pointer can also point to a function , This function have addresses .
    Code:
    int (*Ptr)( );
    int Result();
    Ptr=Result;  // Assign Address of function
    
    This above declaration Pointer to a Function , No Arguments which returns an integer.

    Pointer to a function with arguments .

    Code:
    int (*PtrToFunction) (int  iX, int  iY);
    int SumofIntegers (int iX,int iY);
    PtrToFunction = SumofIntegers;
    
    Function Returning Pointers

    As the function has a return type it can return an int, float or any other data type. Similarly it can return a pointer .
    Code:
    int *ptr;
    int *MyFun();
    ptr=MyFun();
    
    Pointer to an Array

    We have already seen, Pointer to int / pointer to float, can we also have pointer to an array? The answer is yes. See below.
    Code:
    int a[][5]={1,2,3,4,5,6,7,8,9,10};
    int (*Ptr)[5];
    Ptr=a;
    Ptr is a pointer to an array of 5 integers .

    Array of Pointers

    We know that array of int , array of float and so similarly array of pointers. Array of pointers contains collection of addresses. Let us consider the below example

    Code:
    int  *array[3];
    int i=10,j=20,k=30;
    array[0]=&i;
    array[1]=&j;
    array[2]=&k;
    
    Structure Pointer

    We know that pointer pointing to int / char , Similarly Pointer an point to user defined data types like structures / classes. Let us consider the below example

    Code:
    struct sJames
    {
    	int m_iNumber;
    	char *m_szName;
    };
    
    struct sJames Obj={7126,"James"};
    struct sJames *ptr=&Obj;
    cout<<ptr->m_iNumber<<endl;
    cout<<ptr->m_szName<<endl;
    
    Void Pointer

    void pointer is something like pointer pointing to nothing and is a generic pointer. It can be type casted to any other data type.

    Code:
    void *ptr;
    int *p;
    int a=10;
    ptr=&a;
    p=(int *)ptr;
    cout<<*p<<endl;
    
    Const Pointer
    const variable normally tells the compiler that you should not allow modification of a particular variable in the program.

    const char *str1="James"; //String is Constant Pointer is not
    char *const str2="James"; // Pointer is Constant String is not

    Example
    Code:
    char a[]= "prasanna";
    str1 = a; // ok 
    cout << str1<<endl;
    //str2 = a; // illegal 
    str1 = &a[0]; // ok
    
    Null Pointer
    Null pointer is a pointer points to NULL that's equal to integer zero.

    Code:
    int  *Null_Ptr;
    Null_Ptr = NULL; // null pointer 
    
    Note:
    Without initialization is better than empty initialization.

    Memory Leaks

    Memory leak is a big problem using pointers , But if we allocate memory for a particular structure / class / single variable, Proper memory De-allocation is necessary.

    To avoid memory errors using pointers

    1) Memory allocation without de allocation.
    2) With out memory allocation , But de allocation.
    3) Memory allocation , De allocation , But again unnecessary de allocation.
     
  2. coderzone

    coderzone Super Moderator

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    [COMMENT]I have gone through almost all your articles and I really like your articles.Good luck[/COMMENT]
    I guess you are saying the opposite. Its always better to initialize to nothing rather than have it pointed to something.
     
  3. prem_may10

    prem_may10 New Member

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    hi,
    I want to print hello world without using semicolon(;) in the program
     
  4. shabbir

    shabbir Administrator Staff Member

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    Prem, Please put your query as a seperate thread in the Queries and discussion forum. Dont ask your queries as a comments to the articles as that may not eventually get you a reply.
     
  5. aisha.ansari84

    aisha.ansari84 New Member

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  6. rahul.mca2001

    rahul.mca2001 New Member

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    can we type cast a null pointer
     

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