MISRA C:2012 Rule 23.3

A generic selection should contain at least one non-default association

Since R2024a

Description

Rule Definition

A generic selection should contain at least one non-default association.

This rule comes from MISRA C™: 2012 Amendment 3.

Rationale

The default association of a generic selection is selected without any type checking when none of the nondefault associations can be selected. A _Generic statement that consists of only a default association always selects the default selection and is not useful.

Include at-least one nondefault association in a generic selection. If you intend to introduce a constraint violation when the types do not match in a generic selection, omit the default association.

Polyspace Implementation

Polyspace^® reports a violation of this rule if a _Generic statement contains only the default association.

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

expand all

Generic Selection Without Nondefault association

In the example, the _Generic statement get_type_id_only_default consists of only a default association. In the function foo(), invoking this _Generic statement with any type results in selecting the default association. This generic selection is not useful and Polyspace reports a violation.

#define get_type_id(x) ( _Generic((x) /* Compliant */ \
                                , char : 0       \
                                , int  : 1       \
                                ))

#define get_type_id_with_default(x) ( _Generic((x) /* Compliant */ \
                                , char : 0       \
                                , int  : 1       \
                                , default : 3    \
                                ))

#define get_type_id_only_default(x) ( _Generic((x) /* Noncompliant */ \
                                , default : -1   \
                                ))

void foo() {
    int x, y;
    y = get_type_id(x);
    y = get_type_id_with_default(x);
    y = get_type_id_only_default(x);
}

The _Generic statements get_type_id and get_type_id_with_default contain nondefault associations and Polyspace reports no violations.

Check Information

Group: Generic Selections

Category: Advisory

AGC Category: Advisory

Version History

Introduced in R2024a