AUTOSAR C++14 Rule M6-5-2

If loop-counter is not modified by -- or ++, then, within condition, the loop-counter shall only be used as an operand to <=, <, > or >=

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Description

Rule Definition

If loop-counter is not modified by -- or ++, then, within condition, the loop-counter shall only be used as an operand to <=, <, > or >=.

Rationale

If the loop counter increments or decrements by more than one per iteration, avoid using == or != in the loop termination condition. It is unclear from visual inspection if such loop termination conditions are ever satisfied.

For instance, if a loop counter ctr increments by more than one per iteration, such as ctr+=2, and the termination condition is ctr == someVal, the counter might skip the value someVal, resulting in a nonterminating loop.

Nonterminating loops can result in developer confusion or unexpected values.

Polyspace Implementation

Polyspace^® raises this defect whenever all the following are true:

The loop-counter is not modified by -- or ++
The loop-condition does not contain <=, <, > or >=

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

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Nonterminating Loops Created by Using Noncompliant Operand Pairings

#include <cstdint>

uint32_t row, col;

void example()
{
    for (row = 0; row <= 10; row++) {                 //Compliant
        for (col = 100; col != 10; col -= 4) {        //Noncompliant
            //...
        }
    }
    for (row = 0; row != 10; row++) {		    //Compliant
        //...
    }
}

Because the second for loop-counter is not modified by -- or ++, != becomes a noncompliant operand. Use one of the following operands instead: <=, <, > or >=.

Check Information

Group: Statements

Category: Required, Automated

Version History

Introduced in R2019a