MISRA C++:2023 Rule 9.5.1

Legacy for statements should be simple

Since R2024b

Description

Rule Definition

Legacy for statements should be simple. ¹

Rationale

Legacy for statements can introduce side effects that can result in confusion and unexpected results if not accounted for. It is important to review legacy iteration statements and handle all side effects properly. Due to the complexity of this type of review, using the Standard Library algorithms is preferable to using legacy iteration statements. If using a simple for statement, make certain the loop progresses and terminates.

Consider a general legacy for statement:

for(init-statement; condition; increment-statement;) {
   //...
}

A legacy for statement is simple if it meets these criteria, as stated in the MISRA™ C++:2023 standard.

• init-statement only declares and initializes a loop counter of integer type.

• condition uses one of the relational operators <, >, <=, and >= to compare the loop counter to the loop bound.

• You only modify the loop counter by incrementing or decrementing by a loop step within increment-statement.

• The type of the loop bound and loop counter are the same, or if the loop bound is a constant expression, the type of the loop counter has a large enough range to accommodate the value of the loop bound.

• The loop bound and loop step are constant expressions or variables that are not modified within the for statement.

• The loop counter, loop bound, and loop step are neither bound to non-const references nor are their addresses assigned to pointers to non-const values. This ensures that the loop counter, loop bound, and loop step remain unchanged throughout the loop execution.

Use the C++ Standard Library algorithms in place of legacy for statements wherever possible. Use a range-for statement instead of a legacy for statement when iterating over the contents of a container.

This rule does not apply to while and do-while loops.

Polyspace Implementation

Polyspace^® reports a rule violation whenever a legacy for statement that is not simple is used in code. Polyspace uses the definition of simple as detailed in the MISRA™ C++:2023 specifications.

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

Use of Legacy for Statements

The following code contains three examples of legacy for statements.

void example1(int j)
{
    for (int i = 0; i < 10; i = i + j) {         //Noncompliant
        j++;
    }
}

void example2(int depth)
{
    for (int i = 0; i < depth; i++) {            //Compliant  
    }
}

void example3(int depth)
{
    for (int i = 0; i < depth; i++) {            //Noncompliant  
		//...
		depth += 2;
    }
}

• The for-loop in example1() is noncompliant because it modifies the loop step within the body of the loop.

• The for-loop in example2() is compliant because it meets all the MISRA exception criteria for a simple for-loop.

• The for-loop in example3() is noncompliant because it modifies a variable loop bound within the body of the loop.

Check Information

Group: Statements

Category: Advisory

Version History

Introduced in R2024b