The macro expansion should be parenthesized to protect any lower-precedence operators from the surrounding expression. See also \[[PRE00-A. Prefer inline functions to macros]\] and \[[PRE01-A. Use parentheses within macros around parameter names]\]. |
This CUBE() macro definition is non-compliant because it fails to parenthesize the macro expansion.
#define CUBE(X) (X) * (X) * (X) int i = 3; int a = 81 / CUBE(i); |
As a result, the invocation
int a = 81 / CUBE(i); |
expands to
int a = 81 / i * i * i; |
which evaluates as
int a = ((81 / i) * i) * i); /* evaluates to 243 */ |
which is not the desired behavior.
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); |
The problem is not limited to function-like macros.
#define sum a+b /* ... */ int result = sum*4; |
The value of result is a+(b*4) instead of the expected (a+b)*4.
Parenthesizing the macro yields the expected answer.
#define sum (a+b) /* ... */ int result = sum*4; |
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.
\[[Summit 05|AA. C References#Summit 05]\] 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" |