Why is this an issue?
The values that can be represented by a signed bit field with a length of one bit may not meet developer expectations. For example according to the
C99 Standard, Section 6.2.6.2, a single-bit signed bit-field has a single (one) sign bit and no (zero) value bits.
This rule does not apply to unnamed bit fields, as their values cannot be accessed.
Noncompliant code example
signed int f:1; // Noncompliant; there's only room here for the sign
Compliant solution
unsigned int f:1;
or
signed int:1; // unnamed
or
signed int f:2;
Resources
- MISRA C:2004, 6.5 - Bit fields of type signed int shall be at least 2 bits long
- MISRA C:2012, 6.2 - Single-bit named bit fields shall not be of a signed type
- MISRA C++:2008, 9-6-4 - Named bit-fields with signed integer type shall have a length of more than one bit
