C and C++

LANG.STRUCT.CGEN.NOTMACRO : Selection in C Generic not Expanded from Macro Parameters

Summary

One of the following.

Generic selection is not useful in these cases, because the type of the controlling expression is already known locally.

Properties

Class Name Selection in C Generic not Expanded from Macro Parameters
Significance redundancy
Mnemonic LANG.STRUCT.CGEN.NOTMACRO
Categories
MisraC2023 MisraC2023:23.1 A generic selection should only be expanded from a macro
Misra2012 Misra2012:23.1 A generic selection should only be expanded from a macro
Availability Available for C only (not C++).
Enabling Checks for this warning class are disabled by default, and require the unnormalized C ASTs for the project. To enable them, add the following WARNING_FILTER rule and RETAIN_UNNORMALIZED_C_AST specification to the project configuration file. 
RETAIN_UNNORMALIZED_C_AST = Yes
WARNING_FILTER += allow class="Selection in C Generic not Expanded from Macro Parameters"
Note that retaining the unnormalized ASTs will increase the disk space used to store the project representation, and may make the analysis take longer.

Example 

/* ok:
 * - generic selection expanded from function-like macro
 * - macro parameter y expanded into controlling expression
 */
#define PARAM_EXPAND_SIMPLE(y) (_Generic(y,       \
                                         float:1, \
                                         default:0))

/* ok: controlling expression does not have to be ONLY the expanded parameter */
#define PARAM_EXPAND_NONTRIVIAL(y) (_Generic(EXPAND_SIMPLE(y) + 5, \
                                       float:1,          \
                                       default:0))

#define T 5
/* 'Selection in C Generic not Expanded from Macro Parameters' warning issued on following line
 * - generic selection expanded from function-like macro,
 *   BUT
 * - macro's single parameter y is not expanded into controlling expression
 *   (expansions elsewhere are not relevant to this warning class).
 */
#define NO_PARAM_EXPAND(y) (_Generic(T,          \
                                     float:y,    \
                                     default:0) +y )

int lang_struct_cgen_notmacro(int x){
    /* 'Selection in C Generic not Expanded from Macro Parameters' warning issued on following line
     * - generic selection not expanded from a function-like macro.
     */
    return _Generic(x, int:x, default:0);
}

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.