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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 \[[PRE01-A. Use parentheses within macros around variable names]\]. |
Non-Compliant Code Example
This CUBE() macro definition is non-compliant because it fails to parenthesize the macro expansion.
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#define CUBE(X) (X) * (X) * (X) int i = 3; int a = 81 / CUBE(i); |
As a result, the invocation
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int a = 81 / CUBE(i); |
expands to
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int a = 81 / i * i * i; |
which evaluates as
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int a = ((81 / i) * i) * i); /* evaluates to 243 */ |
which is not the desired behavior.
Compliant Solution
By parenthesizing the macro expansion, the CUBE() macro expands correctly (when invoked in this manner).
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#define CUBE(X) ((X) * (X) * (X)) int i = 3; int a = 81 / CUBE(i); |
Risk Assessment
Failing to parenthesize around a function-like macro can result in unexpected arithmetic results.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
PRE02-A | 1 (low) | 1 (unlikely) | 3 (low) | P3 | L3 |
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
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\[[Summit 05|AA. C References#Summit 05]\] 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" |