Lets consider a struct:

struct my_struct {
    char code : 4;
};

This is a POD type. If I write something like this:

my_struct object;

what will be the value od object.code? 0? Or unspecified? Does it
depend on the place of definition (global, local, member)? In my
opinion "object" will be "zero-initialized" which means object.code ==
0. But I could not find in the Standard specific rules for bit
fields...

    And know a class:

class my_class {
private:
    char code : 4;
};

This is not a POD type (since code is private - I hope I remebrer this
well, but if not then lets make my_class not a POD type in a way that
does not interfare with topic of this message - this surly is
possible). If I write something like this:

my_class object;

then again the same questions. And again I think that object.code == 0,
but cannot find specific rules in the Standard.

    Can someone point me the rules for bit fields initialization?

    Adam Badura


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abadura ha scritto:
>     Lets consider a struct:
> 
> struct my_struct {
>     char code : 4;
> };
> 
> This is a POD type. If I write something like this:
> 
> my_struct object;
> 
> what will be the value od object.code? 0? Or unspecified? Does it
> depend on the place of definition (global, local, member)? In my
> opinion "object" will be "zero-initialized" which means object.code ==
> 0. But I could not find in the Standard specific rules for bit
> fields...

In this respect, bit-fields are no different from any other scalar type:
unless initialized, their value is undefined. Notice, however, that any
POD with static storage duration is always zero-initialized, regardless
of the presence or absence of bit-fields.

>     And know a class:
> 
> class my_class {
> private:
>     char code : 4;
> };
> 
> This is not a POD type (since code is private - I hope I remebrer this
> well, but if not then lets make my_class not a POD type in a way that
> does not interfare with topic of this message - this surly is
> possible). If I write something like this:
> 
> my_class object;
> 
> then again the same questions. And again I think that object.code == 0,
> but cannot find specific rules in the Standard.

Even if my_class is not a POD, it has a trivial default constructor. So,
although the object is default initialized by 8.5/9, the effect is the
same as above: the value is undefined if the declaration occurs at local
scope and 0 if it occurs global scope.

>     Can someone point me the rules for bit fields initialization?

There's nothing special in bit fields, they are just scalar types and
covered in 8.5.

Ganesh

      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated.    First time posters: Do this! ]