MISRA C:2012 Rule 14.3

Controlling expressions shall not be invariant

Description

Rule Definition

Controlling expressions shall not be invariant¹ .

Rationale

If the controlling expression, for example an if condition, has a constant value, the non-changing value can point to a programming error.

Polyspace Implementation

The checker reports a violation if the controlling expression of a control statement is always true or false. The control statements that Polyspace^® checks include:

• if, switch

• for, while, do-while

• Ternary (?:) operator

Polyspace Bug Finder™ flags some violations of MISRA C™ 14.3 through the Dead code and Useless if checkers.

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

if condition always true

In this example, a 16-bit unsigned integer u16var is compared to 0xffffu in an if statement. because u16var is a 16-bit unsigned integer, it cannot have a value greater than 0xffffu. The if statement is always true. Polyspace reports a violation of this rule.

#include<stdint.h>

uint16_t u16var;
void foo(){
	if(u16var<=0xffffu){  //Noncompliant
		//...
	}
}

Check Information

Group: Control Statement Expressions

Category: Required

AGC Category: Required

Version History

R2025a: Violation reported on the controlling expression of a switch statement

Polyspace now reports a violation if the controlling expression of a switch statement is always true or always false.

R2024b: Violation reported on the controlling expression of a do-while loop

Polyspace now reports a violation on the controlling expression of a do-while loop if both of these is true:

• The controlling expression evaluates to false.

• The controlling expression does not satisfy the constraints and semantics for an integer constant expression.

For example, the loop expression in this code does not evaluate to false and Polyspace reports a violation.

void h() {
	int s8a = 0;
	do
	{
        //...
	} while((s8a < 10) && (s8a > 20)); // Noncompliant
}

R2023b: More precise implementation of dead code and unnecessary conditional checking

Polyspace now performs a more precise analysis. Unreachable code and unnecessary conditionals are detected with better precision. In addition, the location of the violation is more precise.