AUTOSAR C++14 Rule M5-0-2

Limited dependence should be placed on C++ operator precedence rules in expressions

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Description

Rule Definition

Limited dependence should be placed on C++ operator precedence rules in expressions.

Rationale

Use parentheses to clearly indicate the order of evaluation.

Depending on operator precedence can cause the following issues:

If you or another code reviewer reviews the code, the intended order of evaluation is not immediately clear.
It is possible that the result of the evaluation does not meet your expectations. For instance:
- In the operation *p++, it is possible that you expect the dereferenced value to be incremented. However, the pointer p is incremented before the dereference.
- In the operation (x == y | z), it is possible that you expect x to be compared with y | z. However, the == operation happens before the | operation.

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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Evaluation Order Dependent on Operator Precedence Rules

#include <cstdio>

void showbits(unsigned int x) {
    for(int i = (sizeof(int) * 8) - 1; i >= 0; i--) {
       (x & 1u << i) ? putchar('1') : putchar('0'); // Noncompliant 
    }
    printf("\n");
}

In this example, the checker flags the operation x & 1u << i because the statement relies on operator precedence rules for the << operation to happen before the & operation. If this is the intended order, the operation can be rewritten as x & (1u << i).

Check Information

Group: Expressions

Category: Advisory, Partially automated

Version History

Introduced in R2019a