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Pointer assignment

Since pointers are variables, they can be used without dereferencing. Pointer assignment between two pointers makes them point to the same pointee. So the assignment iq = ip; copies the contents of ip into iq, thus making iq point to whatever ip pointed to. It makes iq point to the same pointee as ip. Pointer assignment does not touch the pointees. It just changes one pointer to have the same reference as another pointer. After pointer assignment, the two pointers are said to be "sharing" the pointee.

Example Consider the following programs:

main() {int i = 3, j = 6; int *p1, *p2;p1 =&i; p2 =&j; *p1 = *p2;} andmain() {int i = 3, j = 6; int *p1, *p2;p1 =&i; p2 =&j; p1 = p2;}

Suppose the values of variables before executing the last assignment are

Variable Address Value
i FFEC 3
j FFEE 6
p1 FFDA FFEC
p2 FFDC FFEE

After the assignment *p1 = *p2; for the first program:

Variable Address Value
i FFEC 6
j FFEE 6
p1 FFDA FFEC
p2 FFDC FFEE

While the assignment p1 = p2 for the second program results

Variable Address Value
i FFEC 3
j FFEE 6
p1 FFDA FFEE
p2 FFDC FFEE

Initializing pointers

Pointer variables with automatic storage duration start with an undefined value, unless their declaration contains an explicit initializer. You can initialize a pointer with the following kinds of initializers:

  • A null pointer constant.
  • A pointer to the same type, or to a less qualified version of the same type.
  • A void pointer, if the pointer being initialized is not a function pointer. Here again, the pointer being initialized can be a pointer to a more qualified type.

Operators on pointers

Besides using assignments to make a pointer refer to a given object or function, you can also modify an object pointer using arithmetic operations. When you perform pointer arithmetic , the compiler automatically adapts the operation to the size of the objects referred to by the pointer type.

You can perform the following operations on pointers to objects:

  • Adding an integer to, or subtracting an integer from, a pointer.
  • Subtracting one pointer from another.
  • Comparing two pointers.

If ip points to the integer x, then *ip can occur in any context where x could, so

*ip = *ip + 10;

The unary operators * and&bind more tightly than arithmetic operators, so the assignment

y = *ip + 1

takes whatever ip points at, adds 1, and assigns the result to y, while

*ip += 1

increments what ip points to, as do

++*ip

and

(*ip)++

The parentheses are necessary in this last example; without them, the expression would increment ip instead of what it points to, because unary operators like * and ++ associate right to left.

When you subtract one pointer from another, the two pointers must have the same basic type, although you can disregard any type. Furthermore, you may compare any pointer with a null pointer constant using the equality operators (== and !=), and you may compare any object pointer with a pointer to void.

Pointer to pointer

A pointer variable is itself an object in memory, which means that a pointer can point to it. To declare a pointer to a pointer , you must use two asterisks, as in the following Example

Questions & Answers

do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Introduction to computer science. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10776/1.1
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