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The macro expansion should always be parenthesized within a function-like macro to protect any lower-precedence operators from the surrounding expression.  See also \[[PRE00-A. Prefer inline functions to macros]\] and \[[PRE01-A. Use parentheses within macros around parameter names]\].

Non-Compliant Code Example

This CUBE() macro definition is non-compliant because it fails to parenthesize the macro expansion.

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which is not the desired behavior.

Compliant Solution

By parenthesizing the macro expansion, the CUBE() macro expands correctly (when invoked in this manner).

#define CUBE(X) ((X) * (X) * (X))
int i = 3;
int a = 81 / CUBE(i);

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Non-Compliant Code Example

The problem is not limited to function-like macros.

#define sum 2+3
int result = sum*4;

The value of result is 14 instead of the expected 20.

 Compliant Solution

Parenthesizing the macro yields the expected answer.

#define sum (2+3)
int result = sum*4;	/* 20 */

 Risk Assessment

Failing to parenthesize around a function-like macro can result in unexpected arithmetic results.

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Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

\[[Summit 05|AA. C References#Summit 05]\] Question 10.1
\[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.10, "Preprocessing directives," and Section 5.1.1, "Translation environment"