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+---- Thread: C90: Bitfield as essential boolean type (/showthread.php?tid=1161)
C90: Bitfield as essential boolean type - nunterberg - 03-03-2015
Is it possible to declare bitfields that can be used as essentially boolean expressions in C90 without vialoating any MISRA rules?
Acording to section D.4, only a bit-field that has been implemented with an essential boolean type is essentially boolean. In C90, such a type does not exist as a "native" type. Sections 8.10.2 and D.6 allow an enumerated type as a way to define an essentially Boolean type. However, using such an enumerated type in a bitfield violates Rule 6.1.
Code:
typedef enum { false, true } bool_t;
struct {
bool_t flag1:1; /* violates Rule 6.1 */
uint16_t flag2:1; /* compliant */
} bf;
if (bf.flag1) { /* compliant? */
do_something();
}
if (bf.flag2) { /* violates Rule 14.4? */
do_something();
}Re: C90: Bitfield as essential boolean type - misra-c - 13-03-2015
You would need to deviate from rule 6.1 if you wish to use an enumeration type as your essentially boolean type.
An alternative would be to define your bool_t as an unsigned int.
Code:
typedef unsigned int bool_t;