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AUTOSAR C++14 Rule M9-6-4

Named bit-fields with signed integer type shall have a length of more than one bit

Since R2020b

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Description

Rule Definition

Named bit-fields with signed integer type shall have a length of more than one bit.

Rationale

Variables that have signed integer bit-field types of length one bit might have values that do not meet developer expectations. For instance, signed integer types of a fixed width such as std16_t have a two's complement representation. In this representation, a single-bit variable has just the sign bit and the variable value might be 0 or -1.

Polyspace Implementation

The checker flags declarations of named variables having signed integer bit-field types of length equal to one.

Bit-field types of length zero are not flagged.

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>

typedef struct
{
   std::uint16_t IOFlag :1;    //Compliant - unsigned type
   std::int16_t InterruptFlag :1; //Noncompliant
   std::int16_t Register1Flag :2; //Compliant - Length more than one bit
   std::int16_t : 1; //Compliant - Unnamed
   std::int16_t : 0; //Compliant - Unnamed
   std::uint16_t SetupFlag :1; //Compliant - unsigned type
} InterruptConfigbits_t;

In this example, only the second bit-field declaration is noncompliant. A named variable is declared with a signed type of length one bit.

Check Information

Group: Classes
Category: Required, Automated

Version History

Introduced in R2020b

See Also

Topics