MISRA.DEFINE.WRONGNAME.C99.2012

A macro shall not be defined with the same name as a keyword

MISRA C 2012 Rule 20.4: A macro shall not be defined with the same name as a keyword

C90 [Undefined 56], C99 [Undefined 98]

Category: Required

Analysis: Decidable, Single Translation Unit

Applies to: C90, C99

Amplification

This rule applies to all keywords, including those that implement language extensions.

Rationale

Using macros to change the meaning of keywords can be confusing. The behaviour is undefined if a standard header is included while a macro is defined with the same name as a keyword.

The following example is non-compliant because it alters the behaviour of the int keyword. Including a standard header in the presence of this macro results in undefined behaviour.

Example

#define int some_other_type 
#include <stdlib.h>

The following example shows that it is non-compliant to redefine the keyword while but it is compliant to define a macro that expands to statements.

#define while( E ) for ( ; ( E ) ; )   /* Non-compliant - redefined while */ 
#define unless( E ) if ( ! ( E ) )     /* Compliant */

#define seq( S1, S2 ) do { \
   S1; S2; } while ( false )           /* Compliant */ 
#define compound( S ) { S; }           /* Compliant */

The following example is compliant in C90, but not C99, because inline is not a keyword in C90.

/* Remove inline if compiling for C90 */ 
#define inline

See also

Rule 21.1