Page 102 - Programming Microcontrollers in C

Structures 87

*(void **) 0xfffc = isr;

places the beginning address of the function isr into the memory
location 0xfffc.
A convenient method of executing this operation is to create a
macro. The following macro definition works:

#define vector(isr, address) (*(void **)(address)=(isr))
Now the function call

vector(timer, 0xffd0);
will place the address of the function named timer into the loca­
tion 0xffd0 in the computer memory map. It is important that
timer be defined as a function that returns a type void.

Structures

Another feature of C not found in many high-level languages is
the structure. A structure is similar to an array, but far more general.
A structure is a collection of one or more variables identified by a
single name. The variables can be of different types. Structures are
types in the sense that an int is a type. Therefore, if you have prop­
erly declared a structure, you may declare another structure of the
same type. Examine the following structure:
struct person
{
char *name;
char *address;
char *city;
char *state;
char *zip
int height;
int weight;
float salary;
};

This structure contains some of the features that describe a per­
son. The person’s name and address are given as pointers to character
strings. The person’s height and weight are integers, and the salary is