MISRA C:2025 Rule 20.7

R2026b

Tokens that look like a preprocessing directive shall not occur within a macro argument

Since R2026b

Description

Tokens that look like a preprocessing directive shall not occur within a macro argument ¹ .

Rationale

If you do not use parentheses, then it is possible that operator precedence does not give the results that you want when macro substitution occurs.

If you are not using a macro parameter as an expression, then the parentheses are not necessary because no operators are involved in the macro.

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

Macro Expressions

#define mac1(x, y) (x * y)
#define mac2(x, y) ((x) * (y))

void foo(void){
    int r;

    r = mac1(1 + 2, 3 + 4);       /* Non-compliant */
    r = mac1((1 + 2), (3 + 4));   /* Compliant */

    r = mac2(1 + 2, 3 + 4);       /* Compliant */
}

In this example, mac1 and mac2 are two defined macro expressions. The definition of mac1 does not enclose the arguments in parentheses. In line 7, the macro expands to r = (1 + 2 * 3 + 4); This expression can be (1 + (2 * 3) + 4) or (1 + 2) * (3 + 4). However, without parentheses, the program does not know the intended expression. Line 8 uses parentheses, so the line expands to (1 + 2) * (3 + 4). This macro expression is compliant.

The definition of mac2 does enclose the argument in parentheses. Line 10 (the same macro arguments in line 7) expands to (1 + 2) * (3 + 4). This macro and macro expression are compliant.

Check Information

Group: Preprocessing Directives

Category: Required

AGC Category: Required

PQL Name: std.misra_c_2025.R20_7

Version History

Introduced in R2026b