Unary minus applied to an unsigned operand
ID |
c.correctness.unary_minus_on_unsigned |
Severity |
low |
Remediation Complexity |
medium |
Remediation Risk |
medium |
Remediation Effort |
low |
Resource |
Numeric Operation |
Language |
C / C++ |
Description
Negating an unsigned value does not produce a negative number: the result wraps around to a very large positive one. Code that reads as a subtraction or a sign flip therefore computes something entirely different. Convert to a signed type of sufficient width before negating, or restructure the expression so the subtraction happens in the right order.
Rationale
Negating an unsigned value does not produce a negative number: the result wraps around to a very large positive one. Code that reads as a subtraction or a sign flip therefore computes something entirely different. Convert to a signed type of sufficient width before negating, or restructure the expression so the subtraction happens in the right order.
The following code illustrates the pattern detected by this rule:
void report(unsigned int count, int delta)
{
// FLAGGED: Unary minus applied to an unsigned operand
unsigned int wrapped = -count;
int negated = -delta;
printf("%u %d\n", wrapped, negated);
}Remediation
Follow secure coding practices and review the references below for detailed remediation guidance.