Parenthesize all variable names in macro definitions. See also [[PRE00-A. Prefer inline functions to macros]] and [[PRE02-A. Macro expansion must always be parenthesized]].
Non-Compliant Code Example
This CUBE() macro definition is non-compliant because it fails to parenthesize the variable names.
#define CUBE(I) (I * I * I) int a = 81 / CUBE(2 + 1);
As a result, the invocation
int a = 81 / CUBE(2 + 1);
expands to
int a = 81 / (2 + 1 * 2 + 1 * 2 + 1); /* evaluates to 11 */
Which is clearly not the desired result.
Compliant Solution
Parenthesizing all variable names in the CUBE() macro allows it to expand correctly (when invoked in this manner).
#define CUBE(I) ( (I) * (I) * (I) ) int a = 81 / CUBE(2 + 1);
Risk Assessment
Failing to parenthesize around the variable names within a macro can result in unexpected arithmetic results.
Rule |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
PRE01-A |
1 (low) |
1 (unlikely) |
3 (low) |
P3 |
L3 |
Examples of vulnerabilities resulting from the violation of this recommendation can be found on the CERT website.
References
[[Summit 05]] Question 10.1
[[ISO/IEC 9899-1999]] Section 6.10, "Preprocessing directives," and Section 5.1.1, "Translation environment"