<< Chapter < Page Chapter >> Page >
A general explanation of pre-processor directives and how they are evaluated by the compiler. Discussed are include and define.

General discussion

A compiler directive is an instruction to the compiler to complete a task before formally starting to compile the program, thus they are sometimes called pre-processor directives. Among other items, during the pre-processor step the compiler is looking for compiler directives and processes them as they are encountered. After completing the tasks as directed, the compiler proceeds to its second step where it checks for syntax errors (violations of the rules of the language) and converts the source code into an object code that contains machine language instructions, a data area, and a list of items to be resolved when he object file is linked to other object files.

Within C++ the pound symbol or # as the first character of a line indicates that the next word is a directive (or command word) to be evaluated. The two most common compiler directives are:

  1. include – with the item following include being the name of a file that is to be inserted at that place in the file. The files are often called "Header Files" because the include directive is normally inserted toward the top of the file (at the head) as one of the first items.
  2. define – with the item followed by an identifier name and a value. This identifier name and value is stored by the compiler and when it encounters the identifier name in the program it substitutes the value for the identifier name.

In the following example the include directive is inserting a file that contains code from the Input-Output Stream library. This file contains necessary code to use cout and cin for sending data to the monitor or getting data from the keyboard.

#include<iostream>

In the next example the define directive is being used to handle a constant (called a defined constant).

Subtituting pi

#define PI 3.14159 ....Later on in the program when it encounters PI....it will replace or substitute PI with the value 3.14159 ....For example:area_circle = radius * radius * PI; would become:area_circle = radius * radius * 3.14159;

Got questions? Get instant answers now!

Of note, compiler directives in C++ do not have a semi-colon after them. Within C++ programming instructions or statements end with a semi-colon, but not compiler directives.

Definitions

compiler directive
An instruction to the compiler to complete a task before formally starting to compile the program.
include
A compiler directive to insert the contents of a file into the program.

Questions & Answers

are nano particles real
Missy Reply
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
Lohitha
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
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
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
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
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
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
Berger describes sociologists as concerned with
Mueller Reply
what is hormones?
Wellington
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Programming fundamentals - a modular structured approach using c++. OpenStax CNX. Jan 10, 2013 Download for free at http://cnx.org/content/col10621/1.22
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Programming fundamentals - a modular structured approach using c++' conversation and receive update notifications?

Ask