Page 81 - Programming Microcontrollers in C

66 Chapter 2 Advanced C Topics

x = *px;

Here the asterisk (*) is a unary operator that applies to a pointer
and directs the compiler to use the integer pointed to by the pointer
px in the assignment. The unary * is referred to as the dereference
operator. With these two operators, it is possible to move from vari­
able to pointer and back again with ease.
A pointer is identified as a pointer to a specific type by state­
ments like

int *px,*pa;
long *pz;
float *pm;

In the above declarations, each of the variables preceded by the
unary asterisk identifies a pointer to the declared type. The pointers
px and pa are the addresses of integers. pz is the address of a long,
and pm is the address of a floating point number. Always remember:
if pk is a pointer to an integer, *pk is an integer. Therefore, the
declarations in the above examples are correct and do define ints,
longs and floats. However, when the compiler encounters the
statement
int *pi;

it provides memory space for a pointer to the type int, but it does
not provide any memory for the int itself. Suppose that a program
has the following declaration:

int m,n;
int *pm;
The statement

m = 10;
pm = &m;
will assign the value 10 to m and put its address into the pointer pm.
If we then make the assignment
n = *pm;

the variable n will have a value 10.
Another interesting fact about pointers is shown in the following
example: