Lesson 6: An introduction to
pointers
Welcome to the sixth in my series of tutorials. This is
one about a topic that you may or
may not have already heard about...pointers. What are
they, what do they do, why do we
care? First, why do we care.
We care about pointers because they allow access to
memory, the also make array-access
faster, they are also somewhat necessary to understand
some functions. Most importantly,
you will see them a lot in other people's code. You may
not need to use them much, but it
will be tremendously important to understand them.
Second, what do they do. Well, I might as well address
this issue as well as what they are
at the same time. Pointers are what they sound
like...pointers. They point to locations
in memory. Picture this: a big jar that holds one thing,
the name of another jar. In the
other jar is the value of an integer. The jars are
memory locations. The jar that holds
the name of the other jar is a pointer. It points to the
other drawer.
How can you use this? Well, look at this little piece of
code:
#include <iostream.h>
void main()
{
int x;
int *pointer;
pointer=&x;
cin>>x;
cout<<*pointer;
}
Guess what! The cout outputs the value in x. Why is
that? Well, look at the code. The
integer is called x. Then a pointer to an integer is
defined as pointer. The astrick(*)
symbol means that it is a pointer. Then I give the
memory location of x to pointer by
using the ampersand(&) symbol. It gives the memory
location of the variable it is in front
of. For example, if the jar that had an integer had a
ampersand in it it would output its
name, or location.
Then the user inputs the value for x. Then the cout uses
the * to put the value stored in
the memory location of pointer. Huh? Picture the jars
again. If the jar with the name of
the other jar in it had a * in front of it it would give
the value stored in the jar with
the same name as the one in the jar with the name. It's
not too hard, the * gives the
value in the location. The unastricked gives the memory
location.
I hope this has been at least an interesting
introduction to pointers. I do not suggest
that you play around with them too much as you can do
unpleasant things on your computer,
but you now should have a better understand of what they
are.
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