MISRA C:2023 Rule 20.11

A macro parameter immediately following a # operator shall not immediately be followed by a ## operator

Since R2024a

Description

Rule Definition

A macro parameter immediately following a # operator shall not immediately be followed by a ## operator¹ .

Rationale

The order of evaluation associated with multiple #, multiple ##, or a mix of # and ## preprocessor operators, is unspecified. Rule 20.10 discourages the use of # and ##. The result of a # operator is a string literal. It is extremely unlikely that pasting this result to any other preprocessing token results in a valid token.

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

Use of # and ##

#define A( x )    #x             /* Compliant */
#define B( x, y ) x ## y         /* Compliant */
#define C( x, y ) #x ## y     /* Non-compliant */

In this example, you can see three uses of the # and ## operators. You can use these preprocessing operators alone (line 1 and line 2), but using # then ## is noncompliant (line 3).

Check Information

Group: Preprocessing Directives

Category: Required

AGC Category: Required

Version History

Introduced in R2024a