Pointers

1. A pointer is a variable which contains the address of variable
You can't assign the address of a short int to a long int

Declare:
int *pt  ;                                                            int *pt = (int*)malloc(sizeof(int) );
int a =10 ;                                                        
 pt = &a;
+ *p -> value of a
+p - >  address of a
+&a -> address of a
+&p -> address of pt

#include <stdio.h>
#include <stdlib.h>
void func0(int i)
{
    i =1;
}
void func1(int *p)
{
    *p = 1;
}
void func2(int *p)
{
    p = (int*)malloc(sizeof(int));
    *p = 1;
}
void func3(int **p)
{
    *p = (int*)malloc(sizeof(int));
    **p = 1;
}
int main()
{
    int i = 0;
    func0(i);
    printf("function0 :%d \n",i);//0
    int *p =(int*)malloc(sizeof(int));
    *p = 0;
    func1(p);
    printf("function1 %d \n",*p);//1
    *p = 0;
    func2(p);
    printf("function2 %d \n",*p);//0
    *p = 0;
    func3(&p);
    printf("function3 %d \n",*p);//1
    return 0;
}

2 . Array and functions
+ value of variables  don't change  before Break out of function  ?
+ what do It return variables  ?

//-------------------------------------------------------------

3.Pointers  and  arrays

int a[10] ;

int *p = &a[0]; 

or int *p = &a;

//-----------------------------------------------------------------------------------

//---------------------------------------------------------------------

string 

The size of pointers 

The size of a pointer is dependent upon the architecture of the computer — a 32-bit computer uses 32-bit memory addresses — consequently, a pointer on a 32-bit machine is 32 bits (4 bytes). On a 64-bit machine, a pointer would be 64 bits (8 bytes). Note that this is true regardless of what is being pointed to:

1 2 3 4 5 6 7 8 9 10 11

char *pchValue; // chars are 1 byte int *pnValue; // ints are usually 4 bytes struct Something {     int nX, nY, nZ; }; Something *psValue; // Something is probably 12 bytes cout << sizeof(pchValue) << endl; // prints 4 cout << sizeof(pnValue) << endl; // prints 4 cout << sizeof(psValue) << endl; // prints 4

As you can see, the size of the pointer is always the same. This is because a pointer is just a memory address, and the number of bits needed to access a memory address on a given machine is always constant. 

( source :http://www.learncpp.com/cpp-tutorial/67-introduction-to-pointers/)

NOTE

*&a = a ;//int   a

int a ; 

int *p ;

p = &a;

*&p = p  ;//which store address of integer i

&*p = &*(&i) //since p = &i

= &(*&i)

= &i

-Within the scope of any variable, value of variable may change but its address will never change in any modification of variable

-

int a[10];                                                   char str[10];
int *pt   ;                                                   char   *ptr ;
pt = a;// pt = &a[0]                                    ptr  = str;// ptr = &str[0];
int  *a[10];                                                int  (*pt)[4];
4.Arrays of pointers
int *a[10];

5. pointers to pointers
int **ptr_to_ptr;

int **ipp ;

int i = 5, j = 6; k = 7;int *ip1 = &i, *ip2 = &j;
when ipp = &ip1;

when *ipp = ip2

when *ipp = &k;

//------------------------------------------------------------------------------------------------------

6. Multidimensional arrays and pointers

*Multi arrays

int a[][];

address of multi- arrays

multi <->multi[0] <->&multi[0][0];

size of multi-arrays

*pointers

- mutli is pointer to mutli[0]

-mutli[0] is  pointer  to mutli[0][0]

=>mutli is pointer to pointer ( pointer const)

- value of multi[0][0]

+ mutli[0][0]

+*mutli[0]

+**multi

*(*(multi + row) + col) and
multi[row][col] 

exam:

int mutli[2][4];

int   (*ptr)[4];

ptr = mutli;

void func(int a[][max], int n , int m);

void func( int (*a)[] , int n , int m);

void  func(int **a , int  n , int m ) ;

//---------------------------------------------------------------------------------------------------------

//---------------------------------------------------------------------------------------------------------

//-----------------------------------------------------------------------------------------------------

7.Pointers to a Function

form: type (*ptr)( type , type);

exam:

int  (*func1)(int x );

void  (*func2)(double x ,  double y);

char  ( *func3)(char *p[]);

void  ( *func4)();

//-----------------------------------------------------------------------------------------------------

//-----------------------------------------------------------------------------------------------------

Note :char (*func)(); >< char *func()

            int  *a[10]   ><   int  (*pt)[4];

To declare a function ( func())  that value return pointer type : type *func();

8. Callback function 

+Example :http://opensourceforu.efytimes.com

+                https://en.wikipedia.org/

                                                                                                                                Thong LT