MISRA C++:2008 Rule 5-0-14

The first operand of a conditional-operator shall have type bool

Description

Rule Definition

The first operand of a conditional-operator shall have type bool.

Rationale

When you use a non-Boolean expression as the first operand of the ? operator, the expression is implicitly converted to bool. Such an implicit conversion might make developer intent unclear and hide errors that lead to bugs that are difficult to diagnose. For instance:

int flag, val;
//...
flag= 1;
val = (flag=0)?2:3;

In the preceding code, it is not clear whether the condition flag = 0 is intended to be an assignment. The compiler casts the return value of the assignment operation into a bool, which is used as the condition for the ? operator. In this case, the developer intent might be to test the value of flag. You might expect val to be 3, but it becomes 2 because of the implicit conversion to bool in the first operand.

Polyspace Implementation

Polyspace^® raises a violation of this rule if a non-Boolean expression is used as the first argument of the ? operator.

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

Avoid Non-Boolean Expression as the First Argument in ? Operator

void foo()
{
    int val, flag;
    flag = 0;
    val = (flag = 0) ? 2 : 3;//Noncompliant
    val = (flag==0)? 2:3; //Compliant
}

In this example, Polyspace flags the non-Boolean expression flag = 0 that is used as the first argument of the ? operator.

Check Information

Group: Expressions

Category: Required

Version History

Introduced in R2013b