Abl-electronic PIC Microcontrollers PIC16 Bedienungsanleitung PDF herunterladen (Seite 137)

Here is a simple example:

// A simple macro which returns greater of its 2 arguments:

#define _MAX(A, B) ((A) > (B)) ? (A) : (B)

// Let's call it:

x = _MAX(a + b, c + d);

/* Preprocessor will transform the previous line into:

x = ((a + b) > (c + d)) ? (a + b) : (c + d) */

It is highly recommended to put parentheses around each of the arguments in

macro body – this will avoid possible problems with operator precedence.

Undefining Macros

You can undefine a macro using the #undef directive.

#undef

macro_identifier

Directive #undef detaches any previous token sequence from the

macro_iden-

tifier

; the macro definition has been forgotten, and the

macro_identifier

undefined. No macro expansion occurs within

#undef lines.

The state of being defined or undefined is an important property of an identifier,

regardless of the actual definition. The

#ifdef and #ifndef conditional direc-

tives, used to test whether any identifier is currently defined or not, offer a flexible

mechanism for controlling many aspects of a compilation.

After a macro identifier has been undefined, it can be redefined with

#define,

using the same or a different token sequence.

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Abl-electronic PIC Microcontrollers PIC16 Bedienungsanleitung Seite 137