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MISRA C++:2008 Rule 7-2-1

An expression with enum underlying type shall only have values corresponding to the enumerators of the enumeration.

Since R2023a

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Description

Rule Definition

An expression with enum underlying type shall only have values corresponding to the enumerators of the enumeration.

Rationale

If your program evaluates an expression with enum underlying type and returns a value that is not part of the enumerator list of the enumeration, the behavior is unspecified.

Compliance with this rule validates the assumption made by other rules in this standard that objects of type enum contain only values corresponding to the enumerators.

To avoid unspecified behavior when evaluating expressions of type enum, use a switch statement. For example:

#include <cstdio>
enum class E : size_t { Pass, Warning, Error };

E Evaluate(size_t input) noexcept {
    E output = E::Pass;
    switch (input) {
      case 0: {
          output = E::Pass;
          break;
      }
      case 1: {
          output = E::Warning;
          break;
      }
      case 2: {
          output = E::Error;
          break;
      }
      default: {
          output = static_cast<E>(0);
      }
    }
    return output;
}

Polyspace Implementation

Polyspace® flags the use of a value that is not part of the enumerators of an enumeration.

Polyspace does not flag the use of unknown values, even if you do not check the range of the value before you use it in the enum expression.

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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#include <cstdint>

enum class Suit : uint8_t { None = 1, Diamonds, Clubs, Hearts, Spades };

Suit resetRedSuit(uint8_t card) noexcept {
    Suit hand = Suit::None;
    if(card < 6){ //check range of card is inside Suit enum
        hand = static_cast<Suit>(card);
    }

    if (hand == Suit::Diamonds ||
        hand == Suit::Hearts) {
            hand = static_cast<Suit>(0); // Noncompliant
    }
    return hand;
}

In this example, Polyspace flags the second static_cast in function resetRedSuit because the expression uses a value (0) that is not part of the enumerator list of enumeration Suit.

Check Information

Group: Declarations
Category: Required

Version History

Introduced in R2023a

See Also

Topics