SEI CERT C Coding Standard

Preprocessor (PRE) - PRE31-C. Avoid side effects in arguments to unsafe macros
}
/* ... */
Note the comment warning programmers that the macro is unsafe. The macro can also be renamed
ABS_UNSAFE() to make it clear that the macro is unsafe. This compliant solution, like all
the compliant solutions for this rule, has undefined behavior if the argument to ABS() is equal to
the minimum (most negative) value for the signed integer type. (See INT32-C. Ensure that operations
on signed integers do not result in overflow for more information.)
2.2.3 Compliant Solution
This compliant solution follows the guidance of PRE00-C. Prefer inline or static functions to
function-like macros by defining an inline function iabs() to replace the ABS() macro. Unlike
the ABS() macro, which operates on operands of any type, the iabs() function will truncate arguments
of types wider than int whose value is not in range of the latter type.
#include
#include
static inline int iabs(int x) {
return (((x) < 0) ? -(x) : (x));
}
void func(int n) {
/* Validate that n is within the desired range */
int m = iabs(++n);
}
/* ... */
2.2.4 Compliant Solution
A more flexible compliant solution is to declare the ABS() macro using a _Generic selection.
To support all arithmetic data types, this solution also makes use of inline functions to compute
integer absolute values. (See PRE00-C. Prefer inline or static functions to function-like macros
and PRE12-C. Do not define unsafe macros.)
According to the C Standard, 6.5.1.1, paragraph 3 [ISO/IEC 9899:2011]:
The controlling expression of a generic selection is not evaluated. If a generic selection
has a generic association with a type name that is compatible with the type of the controlling
expression, then the result expression of the generic selection is the expression
in that generic association. Otherwise, the result expression of the generic selection is
the expression in the default generic association. None of the expressions from any
other generic association of the generic selection is evaluated.
SEI CERT C Coding Standard: Rules for Developing Safe, Reliable, and Secure Systems 26
Software Engineering Institute | Carnegie Mellon University
[DISTRIBUTION STATEMENT A] Approved for public release and unlimited distribution.