<< Chapter < Page Chapter >> Page >
iPtr =&iVar; // Let iPtr point to the variable iVar.

In a pointer declaration, the asterisk (*) is part of an individual declarator. We can thus define and initialize the variables iVar and iPtr in one declaration, as follows:

int iVar = 77, *iPtr =&iVar; // Define an int variable and a // pointer to it.

The second of these two declarations initializes the pointer iPtr with the address of the variable iVar, so that iPtr points to iVar. Figure 4.1. illustrates one possible arrangement of the variables iVar and iPtr in memory. The addresses shown are purely fictitious examples. As Figure 4.1. shows, the value stored in the pointer iPtr is the address of the object iVar.

A pointer and another object in memory

It is often useful to output addresses for verification and debugging purposes. The printf() functions provide a format specifier for pointers: %p. The following statement prints the address and contents of the variable iPtr:

printf("Value of iPtr (i.e. the address of iVar): %p\n" "Address of iPtr: %p\n", iPtr,&iPtr);

The size of a pointer in memory given by the expression sizeof(iPtr)

&And * operators

The unary operator&gives the address of an object, so the statement

p =&c;

assigns the address of c to the variable p, and p is said to “point to” c. The&operator only applies to objects in memory: variables and array elements. It cannot be applied to expressions, constants, or register variables.

* is the operator that retrieves the value stored at the address held in the pointer. The indirection operator * yields the location in memory whose address is stored in a pointer. If ptr is a pointer, then *ptr designates the object that ptr points to. Using the indirection operator is sometimes called dereferencing a pointer. The type of the pointer determines the type of object that is assumed to be at that location in memory. For example, when you access a given location using an int pointer, you read or write an object of type int.

The indirection operator * is a unary operator; that is, it has only one operand.ptr points to the variable x. Hence the expression *ptr is equivalent to the variable x itself.

double x, y, *ptr; // Two double variables and a pointer to double. ptr =&x; // Let ptr point to x. *ptr = 7.8; // Assign the value 7.8 to the variable x.*ptr *= 2.5; // Multiply x by 2.5. y = *ptr + 0.5; // Assign y the result of the addition x + 0.5.
Got questions? Get instant answers now!

Do not confuse the asterisk (*) in a pointer declaration with the indirection operator. The syntax of the declaration can be seen as an illustration of how to use the pointer.

double *ptr;

As declared here, ptr has the type double * (read: "pointer to double"). Hence the expression *ptr would have the type double.

Of course, the indirection operator * must be used with only a pointer that contains a valid address. This usage requires careful programming! Without the assignment ptr =&x in the listing above, all of the statements containing *ptr would be senseless dereferencing an undefined pointer value and might well cause the program to crash.

Questions & Answers

I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Introduction to computer science. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10776/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Introduction to computer science' conversation and receive update notifications?

Ask