The C Programming Language - Pointers

1 Pointers
Pointers are a very important tool in the C programming language. Basically, a pointer
is nothing more than a variable that stores the memory address of another variable.
So, pointers only store the address of a memory object of a certain data type.
If you've worked with functions, you may have thought that it would be handy if you
could return more than one value to the calling function.
This is easily done with a pointer. In this case, you need to pass the address, that is, a
pointer to a specific memory location, to the function. You can now use this address
to write a desired value to the memory location specified in the function. You have
now overwritten the variable at the corresponding memory location with a new value
and can also use this variable outside the function.
Another advantage of pointers is the saving of copying operations and the associated
saving of computing time. Suppose you have a function to which you pass ten integer
values. With a 16-bit system, you have to pass 10 x 2 bytes here. But if you use a pointer
here, you only pass a pointer to the beginning of an array of these ten integer values.
And for this pointer you need only 2 bytes of memory.
Also, memory areas can be dynamically manipulated with pointers. You can pass data
objects by reference to functions, and you can use pointers to implement complex data
structures like lists.
So, pointers contain a memory address of a certain expected data type, e.g. char, int,
float, etc. A pointer points directly to a specific address in memory. Pointers are
dereferenced with the * operator. The & operator returns the address of an element
to which the & operator is applied.
Let's first look at how a variable is stored in memory:
int a = 2;
Here the variable a of data type integer has been initialized with the value 2. In this
example, this variable was stored in RAM, e.g., at address 0x015A.
Name Address Value
a 0x015A 2
The C Programming Language by Heimo Gaicher – Chapter Pointers 6