Parenthesize all variable names in macro definitions. See also \[[PRE00-A. Prefer inline functions to macros|PRE00-A. Prefer inline functions to macros]\] and \[[PRE02-A. Macro expansion must always be parenthesized|PRE02-A. Macro expansion must always be parenthesized]\]. |
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.
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); |
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.
\[[Summit 05|AA. C References#Summit 05]\] 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" |