Abl-electronic PIC Microcontrollers PIC16 Manuel d'utilisateur télécharger pdf (Page 141)

Directives #if, #elif, #else, and #endif

The conditional directives #if, #elif, #else, and #endif work very similar to

the common C conditional statements. If the expression you write after the #if

has a nonzero value, the line group immediately following the #if directive is

retained in the translation unit.

Syntax is:

#if

constant_expression_1

section_1

[#elif

constant_expression_2

section_2

...

[#elif

constant_expression_n

section_n

[#else

final_section

#endif

Each #if directive in a source file must be matched by a closing #endif direc-

tive. Any number of #elif directives can appear between the #if and #endif

directives, but at most one #else directive is allowed. The #else directive, if

present, must be the last directive before

#endif.

The sections can be any program text that has meaning to the compiler or the pre-

processor. The preprocessor selects a single section by evaluating the

constant_expression

following each #if or #elif directive until it finds a

true (nonzero) constant expression. The

constant_expressions

are subject to

macro expansion.

If all occurrences of constant-expression are false, or if no

#elif directives

appear, the preprocessor selects the text block after the

#else clause. If the

#else clause is omitted and all instances of

constant_expression

in the #if

block are false, no section is selected for further processing.

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Abl-electronic PIC Microcontrollers PIC16 Manuel d'utilisateur Page 141

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