Objective-C Pointers

iPhone Monday, April 06, 2015

How Use Pointers in Objective-C

Pointers in Objective-C are simple and enjoyable to learn. Some Objective-C programming undertakings are performed all the more effectively with pointers, and different errands, for example, dynamic memory designation, can't be performed without utilizing pointers. So it gets to be important to learn pointers to turn into a flawless Objective-C developer. How about we begin learning them in straightforward and simple steps.

As you know, each variable is a memory area and each memory area has its address characterized which can be gotten to utilizing ampersand (&) administrator, which indicates a location in memory. Consider the accompanying sample, which will print the location of the variables characterized:

#import <Foundation/Foundation.h>;

int main ()
{
int var1;
char var2[10];

NSLog(@"Address of var1 variable: %x\n", &var1 );
NSLog(@"Address of var2 variable: %x\n", &var2 );

return 0;
}

At the point when the above code is accumulated and executed, it delivers the outcome something as takes after:

2013-09-13 03:18:45.727 demo[17552] Address of var1 variable: 1c0843fc
2013-09-13 03:18:45.728 demo[17552] Address of var2 variable: 1c0843f0

Thus, you comprehended what is memory location and how to get to it, so base of the idea is over. Presently give us a chance to see what is a pointer.

What Are Pointers?

A pointer is a variable whose quality is the location of another variable, i.e., direct address of the memory area. Like any variable or steady, you must announce a pointer before you can utilize it to store any variable location. The general manifestation of a pointer variable announcement is:

type *var-name;

Here, sort is the pointer's base sort; it must be a legitimate Objective-C information sort and var-name is the name of the pointer variable. The reference mark * you used to pronounce a pointer is the same indicator that you use for duplication. Be that as it may, in this announcement the reference bullet is being utilized to assign a variable as a pointer. Taking after are the substantial pointer announcement:

int    *ip;    /* pointer to an integer */
double *dp;    /* pointer to a double */
float  *fp;    /* pointer to a float */
char   *ch     /* pointer to a character */

The real information kind of the estimation of all pointers, whether whole number, buoy, character, or something else, is the same, a long hexadecimal number that speaks to a memory address. The main distinction between pointers of diverse information sorts is the information sort of the variable or steady that the pointer focuses to.

How to use Pointers?

There are couple of imperative operations, which we will do with the assistance of pointers much of the time. (a) we characterize a pointer variable, (b) allot the location of a variable to a pointer, and (c) at last get to the quality at the location accessible in the pointer variable. This is carried out by utilizing unary administrator * that profits the estimation of the variable found at the location indicated by its operand. Taking after illustration makes utilization of these operations:

#import <Foundation/Foundation.h>;

int main ()

{

int var = 20; /* actual variable declaration */

int *ip; /* pointer variable declaration */

ip = &var; /* store address of var in pointer variable*/

NSLog(@"Address of var variable: %x\n", &var );

NSLog(@"Address stored in ip variable: %x\n", ip );

NSLog(@"Value of *ip variable: %d\n", *ip );

return 0;

}

At the point when the above code is accumulated and executed, it creates the outcome something as takes after:

2013-09-13 03:20:21.873 demo[24179] Address of var variable: 337ed41c
2013-09-13 03:20:21.873 demo[24179] Address stored in ip variable: 337ed41c
2013-09-13 03:20:21.874 demo[24179] Value of *ip variable: 20

NULL Pointers in Objective-C

It is dependably a decent practice to allot a NULL quality to a pointer variable in the event that you don't have accurate location to be alloted. This is carried out at the time of variable presentation. A pointer that is alloted NULL is known as an invalid pointer.

The NULL pointer is a consistent with an estimation of zero characterized in a few standard libraries. Consider the accompanying project:

#import <Foundation/Foundation.h>;

int main ()

{

int *ptr = NULL;

NSLog(@"The value of ptr is : %x\n", ptr );

return 0;

}

At the point when the above code is aggregated and executed, it creates the accompanying result:

2013-09-13 03:21:19.447 demo[28027] The value of ptr is : 0

On the vast majority of the working frameworks, projects are not allowed to get to memory at address 0 in light of the fact that that memory is saved by the working framework. Then again, the memory address 0 has exceptional hugeness; it flags that the pointer is not expected to indicate an open memory area. Be that as it may by tradition, if a pointer contains the invalid (zero) quality, it is expected to indicate nothing.

To check for an invalid pointer, you can utilize an if proclamation as takes after:

if(ptr)     /* succeeds if p is not null */
if(!ptr)    /* succeeds if p is null */