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This diagnostic rule is based on the MISRA (Motor Industry Software Reliability Association) software development guidelines.
This diagnostic rule is relevant only for C.
A bit field should not be declared as a data member of a union. The way bit fields are stored in user-defined types is implementation-defined. If two bit fields with the same type are declared one after another, the compiler is not obligated to optimize their location in a single memory block. As a result, it is not clear which bits of a previously stored value the bit field will access.
The code example for which the analyzer issues warnings:
union U1
{
int a : 8; // <=
int b;
};
union U2
{
int a : 8; // <=
int b : 24; // <=
};The rule does not apply to subobjects within a union that are not themselves unions.
union U3
{
struct
{
int a:4;
int b:4;
} c;
int d;
};This diagnostic rule is classified as:
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