Rule Definition
Explicitly declaring a bit-field unsigned prevents unexpected sign extension, overflows and implementation-defined behavior. Note that if a bit-field has enumeration type, then the enumeration base needs to be declared of an explicitly unsigned type.

Remediation
Make sure bit fields are unsigned type or Enums with base defined as unsigned

Violation Code Sample

#include <cstdint>
enum class E1 : std::uint8_t
{
E11,
E12,
E13
};
enum class E2 : std::int16_t
 {
 E21,
 E22,
 E23
 };
 enum class E3
 {
 E31,
 E32,
 E33
 };
 enum E4
 {
 E41,
 E42,
 E43
 };
 class C
 {
 public:
 std::int32_t a : 2; // Non-compliant - signed integral type
 bool c : 1; // Non-compliant - it is implementation-defined whether bool is
 // signed or unsigned
 char d : 2; // Non-compliant
 wchar_t e : 2; // Non-compliant
 E2 f2 : 2; // Non-compliant - E2 enum class underlying type is signed
 // int
 E3 f3 : 2; // Non-compliant - E3 enum class does not explicitly define
 // underlying type
 E4 f4 : 2; // Non-compliant - E4 enum does not explicitly define underlying
 // type
 }

Fixed Code Sample

#include <cstdint>
enum class E1 : std::uint8_t
{
E11,
E12,
E13
};
enum class E2 : std::int16_t
 {
 E21,
 E22,
 E23
 };
 enum class E3
 {
 E31,
 E32,
 E33
 };
 enum E4
 {
 E41,
 E42,
 E43
 };
 class C
 {
 public:
 std::uint8_t b : 2U; // Compliant

 E1 f1 : 2; // Compliant

 }

AUTOSAR C++ 2014, A9-6-1: Bit-fields shall be either unsigned integral or enumeration (with underlying type of unsigned integral type). JSF December 2005 [7]: AV Rule 154 Bit-fields shall have explicitly unsigned integral or enumeration types only. HIC++ v4.0 [8]: 9.2.1 Declare bit-fields with an explicitly unsigned integral or enumeration type. https://cwe.mitre.org/data/definitions/190.html