Getting Started

Chapter 6: C Functions and Program Structures

e possible source of problems occurs when you reuse a token. You might write:

efine Up 0

d come back a month later, when your header file has 500 lines and forget that

d Up and add:

1

and you won’t get any warnings, other than

me mysterious bugs that you’ll blame on the

see what you’ve done and apply a well-

serve

tion

a complex, or frequently

ine the larger of two

) : (y) )

7;

t c = 0;

( a, b);

ompiler sees.

bstituted

a function is located in only one place

e big difference from a microcontroller

at nothing is pushed on the stack when a macro is used, unlike

On

#d

An
you have already define

#define Up

The preprocessor uses the last #define
this one. But you probably will get so
hardware until much later you finally
de d boink to your own head.

Macro Substit
e can se #de

u
W u fine to make a simple token that replaces
used expression. For example we may want to determ
variables:

#define larger( x, y) ( (x)>(y)? (x

Which we wou use ald s:

int a=
nt b =

9;
i
in

c = larger

The preprocessor replaces the last statement with:

c = ( (a)>(b)? (a) : (b) );

Which is what the c

The expression larger( a, b) looks like a function but isn’t. A macro is su
in the code anywhere that it is used, wh
ch time it is used. Th

ile
and is called ea
perspective is th