QA·C Help - 4115

	4115	Operand of logical && or \|\| operator is not an 'essentially Boolean' expression.

Arithmetic type - Operands		REFERENCE - ISO:C90-6.3.13 Logical AND Operator, ISO:C90-6.3.14 Logical OR Operator

An operand of this logical && or logical || operator is not an effectively Boolean expression.

The ISO;C90 language does not support an explicitly Boolean type. Type _Bool was introduced in ISO:C99 but is not recognised in the current version of QAC. In both versions of the language, there exist a number of operators which always yield a value of either 0 or 1 which is of type int. These operators are:

the relational operators: < > <= >=
the equality operators: == !=
the logical operators: ! && ||

Although these operators yield a value of type int, the underlying type may be considered to be effectively.boolean.

The logical operators && and || not only yield a result of effectively Boolean type; they also interpret their operands in a Boolean sense by comparing them with 0. According to the ISO:C standard, these operands can be of any scalar type. However, message 4115 is generated whenever the underlying type of an operand is NOT effectively Boolean.

So, for example, rather than using an integer variable, e.g. "x" as an operand, it may be preferable to use the expression "x != 0", so that the logical comparison is made explicit and more readable.

For example:


/*PRQA S 1278,2017,2213,3120,3198,3199,3203,3408,3447 ++*/

extern unsigned int ui;
extern unsigned int uj;

extern void foo(void)
{
    if ((ui != 0U) && (uj > 0U)) { }        /*              */
    if ((ui > 10U) || uj) { }               /* Message 4115 */
    return;
}

MISRA-C:2004 Rules applicable to message 4115:

Rule 12.6 (Advisory)

The operands of logical operators (&&, || and !) should be effectively Boolean. Expressions that are effectively Boolean should not be used as operands to operators other than (&&, ||, !, =, ==, != and ?:).