User manual

C Language Features
 2012 Microchip Technology Inc. DS52053B-page 211
The type and conversion of numeric values in the preprocessor domain is the same as
in the C domain. Preprocessor values do not have a type, but acquire one as soon as
they are converted by the preprocessor. Expressions may overflow their allocated type
in the same way that C expressions may overflow.
Overflow may be avoided by using a constant suffix. For example, an L after the num-
ber indicates it should be interpreted as a long once converted.
So for example
#define MAX 1000*1000
and
#define MAX 1000*1000L
will define the values 0x4240 and 0xF4240, respectively.
TABLE 5-11: PREPROCESSOR DIRECTIVES
Directive Meaning Example
# Preprocessor null directive, do nothing #
#assert Generate error if condition false #assert SIZE > 10
#asm Signifies the beginning of inline assem-
bly
#asm MOVLW FFh
#endasm
#define Define preprocessor macro #define SIZE 5
#define FLAG
#define add(a,b) ((a)+(b))
#elif Short for #else #if see #ifdef
#else Conditionally include source lines see #if
#endasm Terminate inline assembly see #asm
#endif Terminate conditional source inclusion see #if
#error Generate an error message #error Size too big
#if Include source lines if constant
expression true
#if SIZE < 10
c = process(10)
#else
skip();
#endif
#ifdef Include source lines if preprocessor
symbol defined
#ifdef FLAG
do_loop();
#elif SIZE == 5
skip_loop();
#endif
#ifndef Include source lines if preprocessor
symbol not defined
#ifndef FLAG
jump();
#endif
#include Include text file into source #include <stdio.h>
#include “project.h”
#line Specify line number and filename for
listing
#line 3 final
#nn (Where nn is a number) short for
#line nn
#20
#pragma Compiler specific options Refer to Section 5.14.4 “Pragma
Directives”
#undef Undefines preprocessor symbol #undef FLAG
#warning Generate a warning message #warning Length not set