[previous] MISRA-C:2004  Rule  19.11:  (Required) [next] All macro identifiers in preprocessor directives shall be defined before use, except in #ifdef and #ifndef preprocessor directives and the defined() operator.
If an attempt is made to use an identifier in a preprocessor directive, and that identifier has not been defined, the preprocessor will sometimes not give any warning but will assume the value zero. #ifdef, #ifndef and defined() are provided to test the existence of a macro, and are therefore excluded.

For example: 

#if x < 0           /* x assumed to be zero if not defined */

Consideration should be given to the use of a #ifdef test before an identifier is used.

Note that preprocessing identifiers may be defined either by use of #define directives or by options specified at compiler invocation. However the use of the #define directive is preferred.

QAC messages that encompass this guideline:

3332 The macro '%s' used in this '#if' or '#elif' expression is not defined.


(c) The Motor Industry Research Association, 2004
QA C Source Code Analyser 8.1.2
MISRA-C:2004 Compliance Module 3.2
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