MISRA C++:2008 Rule 4-5-1

Expressions with type bool shall not be used as operands to built-in operators other than the assignment operator =, the logical operators &&, ||, !, the equality operators == and !=, the unary & operator, and the conditional operator

Description

Rule Definition

Expressions with type bool shall not be used as operands to built-in operators other than the assignment operator =, the logical operators &&, ||, !, the equality operators == and !=, the unary & operator, and the conditional operator.

Rationale

Operators other than the ones mentioned in the rule do not produce meaningful results with bool operands. Use of bool operands with these operators can indicate programming errors. For instance, you intended to use the logical operator || but used the bitwise operator | instead.

Polyspace Implementation

Polyspace^® reports a violation of this rule if a boolean type is used as operands to operators other than these:

• =

• &&

• ||

• !

• ==

• !=

• unary & and ?

Troubleshooting

If you expect a rule violation but Polyspace does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Compliant and Noncompliant Uses of bool Operands

void boolOperations() {
    bool lhs = true;
    bool rhs = false;
    
    int res;
    
    if(lhs & rhs) {} //Noncompliant
    if(lhs < rhs) {} //Noncompliant
    if(~rhs) {}      //Noncompliant
    if(lhs ^ rhs) {} //Noncompliant
    if(lhs == rhs) {} //Compliant
    if(!rhs) {}       //Compliant
    res = lhs? -1:1;  //Compliant  
}

In this example, bool operands do not violate the rule when used with the ==, ! and the ? operators.

Check Information

Group: Standard Conversions

Category: Required

Version History

Introduced in R2013b

R2024b: Using assignment operator with boolean and floating-point values

Polyspace no longer reports a violation when assigning a float or double to a bool value.

bool getBool();

void example() {
	double x;

	x = getBool();    //Compliant
}