C++ Pointers-Concept Explained

Deepika Bansal · 2011-08-16T01:40:59+00:00

C++ pointer or simply a pointer is a simple variable that has the capability to store the memory address of some location. Lets discuss a small program for illustration: int * p; int q=10; p=&q; cout<<"Address of q is: "<<p<<endl; cout<<"Value of q is: "<<*p<<endl; Here p is a pointer variable and q is a simple interger variable. & is the address operator. So when we've the statement p=&q, we are actually initializing p with the memory address of q. As memory addresses are generally of hexadecimal type, so p now also has some hexadecimal value. p as such has no data type. But int *p means that the data type of the contents of memory location referenced by p (i.e. q) is interger. So p is also called pointer to integer. Displaying p will display the memory address of the variable q. *p displays the content of the memory location it refers to i.e. value of q.

C++ Pointers-Concept Explained

Deepika Bansal

Member

Updated: Oct 5, 2024

Views: 978
C++ pointer or simply a pointer is a simple variable that has the capability to store the memory address of some location.

Lets discuss a small program for illustration:
```
int * p;
int q=10;
p=&q;
cout<<"Address of q is: "<<p<<endl;
cout<<"Value of q is: "<<*p<<endl;
```
- Here p is a pointer variable and q is a simple interger variable.
- & is the address operator. So when we've the statement p=&q, we are actually initializing p with the memory address of q.
- As memory addresses are generally of hexadecimal type, so p now also has some hexadecimal value.
- p as such has no data type. But int *p means that the data type of the contents of memory location referenced by p (i.e. q) is interger.
- So p is also called pointer to integer.
- Displaying p will display the memory address of the variable q.
- *p displays the content of the memory location it refers to i.e. value of q.
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Deepika Bansal

Member • Aug 16, 2011

Lets consider the following as well:
&*p is same as &(*p) which means address of the value stored.
*&*p is same as *(&(*p)) which means value of variable through pointer p.
*&p is same as *(&p) which means value of pointer.

This means we always resolve such expressions from the inwards and moving outwards.

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Deepika Bansal

Member • Aug 16, 2011

Pointer Expression

int x=5,y=5;
int *p, *q;
int a,b,c,d;
p=&x;               //p now contains the memory address of x ie p refers to x
q=&y;              //q now contains the memory address of y ie q refers to y
a=(*p)+(*q);   //x+y
b=(*p)-(*q);   //x-y
c=(*p)*(*q);   //x*y
 d=(*p)/(*q);   //x/y
*p=*p+10;     // x=x+10

Here we are accessing the value of x and y using the pointers p and q as *p and *q respectively.

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Deepika Bansal

Member • Aug 16, 2011
Scale Factor
We can also have something like p++ or p--.
```
int *p;
int x=10;
p=&x;
p++;
```
Here when we are incrementing or decrementing the pointer variable p is according to the data type of the variable it is pointing to i.e. x in our case.
In our example we are considering x to be of type int. Int type requires 2 bytes of memory location to store one integer value. So when we're having p++, we are actually moving two bytes so that p may now point to next integer value (which may be a garbage value as well).

Had p be of type char *, p would have been incremeted by 1 byte to point to next char.
Similarly for float *, p would have been incremented by 4 bytes to point to next float and so on.

So the key formula is:
ptr++ is same as ptr=ptr+1 which in turn is equivalent to ptr=ptr + (1*size of element).

PS: Division and Multiplication is not applicable this way.
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