A7-2-1 - Unofficial Autosar C++ Guidelines Reference

Rule A7-2-1 (required, implementation, automated)

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

Rationale

It is unspecified behavior if the evaluation of an expression with enum underlying type yields a value which does not correspond to one of the enumerators of the enumeration.

Additionally, other rules in this standard assume that objects of enum type only contain values corresponding to the enumerators. This rule ensures the validity of these assumptions. One way of ensuring compliance when converting to an enumeration is to use a switch statement.

Example

// $Id: A7-2-1.cpp 289436 2017-10-04 10:45:23Z michal.szczepankiewicz $
#include <cstdint>
enum class E : std::uint8_t
{
Ok = 0,
Repeat,
Error
};
E Convert1(std::uint8_t number) noexcept
{
E result = E::Ok; // Compliant
switch (number)
{
case 0:
{
result
= E::Ok; // Compliant
break;
}
case 1:
{
result = E::Repeat; // Compliant

break;
}
case 2:
{
result
= E::Error; // Compliant
break;
}
case 3:
{
constexpr std::int8_t val = 3;
result
= static_cast<E>(val); // Non-compliant - value 3 does not
// correspond to any of E’s
// enumerators
break;
}
default:
{
result
=
static_cast<E>(0); // Compliant - value 0 corresponds to E::Ok
break;
}
}
return result;
}
E Convert2(std::uint8_t userInput) noexcept
{
E result = static_cast<E>(userInput); // Non-compliant - the range of
// userInput may not correspond to
// any of E’s enumerators
return result;
}
E Convert3(std::uint8_t userInput) noexcept
{
E result = E::Error;
if (userInput < 3)
{
result = static_cast<E>(userInput); // Compliant - the range of
// userInput checked before casting
// it to E enumerator
}
return result;
}

Unofficial Autosar C++ Guidelines Reference

Rationale

Example

See also