bit field initialization

[David Rubin]

Can bit fields be initialized with an initializer list, particularly if they are
fields of a structure?

struct {
int a : 1;
int b : 3;
int c : 5;
int d : 7;
} foo = {0, 2, 30, 120};

/david

 

[Eric Sosman]

Can bit fields be initialized with an initializer list, particularly if they are
fields of a structure?

struct {
int a : 1;
int b : 3;
int c : 5;
int d : 7;
} foo = {0, 2, 30, 120};

Yes. However, note that it's implementation-defined
whether a plain `int' bit-field is signed or unsigned, so
the initializers for `c' and `d' may be too large. For
the same reason, `a' might be incapable of holding any
value other than zero.

If you want to use bit fields (which, IMHO, are less
useful than their appearance suggests), I'd recommend
writing `unsigned int' or `signed int' explicitly instead
of trusting to the implementations' whims.