"Kevin Goodsell" <usenet1.spamfree.fusion@neverbox.com> wrote in message
news:3f3401f4@shknews01...

Sims wrote:

const int aa = 1;
const int ab = 2;
const int ac = 4;

int someval = aa | ab | ac;

if( someval & ab )
{
// do this
}

if( someval & ab != 0 )
{
// do this
}

[...] So your two examples are equivalent.

Not quite. operator!= will be evaluated before operator& (binary).

Yes, it is not 0. Converted to bool, you get true.

Does the standard say that i am right or should i have written?

if( someval & ab != 0 )
{
// do this
}

Is my compiler wrong in accepting this?

No, but it does not do what you (most probably) intended. 'ab != 0' is
first evaluated, then the result is and'd with someval. The result of that
is converted to bool. Write it as:

if( (someval & ab) != 0 )

and you have the same as the first example.

My second question, is, if i have a structure
typedef struct
{
char a
int b
}MYSTRUCT *PMYSTRUCT

Other than you forgot all ";", I would recommend writing it like this:

struct MYSRUCT
{
char a;
int b;
};

and i Read(..) a file using sizeof( MYSTRUCT ) will it make a

if

i had declared my structure as
typedef struct
{
int b
char a
}MYSTRUCT *PMYSTRUCT

Yes. You switched the variables and will probably get garbage.

and what about a structure like
typedef struct
{
int b
char a
ANOTHERSTRUCT * B
}MYSTRUCT *PMYSTRUCT

how can i get 'sizeof' when ANOTHERSTRUCT is only a pointer?

sizeof is a compile time operator. It returns the size of what a
type/variable will occupy in memory, including all padding bits and bytes.
If you want to know the overall size of the structure (exluding padding
bytes), create a member function 'size' which returns the size:

return sizeof (a) + sizeof (b) + sizeof (*B);

Or, if you want the real amount of memory that the structure takes,
including the memory pointed by, return this:

return sizeof (*this) + sizeof (*B);

where do i get 'ANOTHERSTRUCT ' size?

sizeof (ANOTHERSTRUCT) would do. Or, if that struct contains pointers

well, you should provide a 'size' function for that structure as well.

where is it stored, in another segment?

I do not think C++ has a concept of segments. Just know that when you

hth

I am sorry, what? 'someval & ab' extracts only one bit. If that bit
is not zero, you get your 'if'. If the bit _is_ 0, it doesn't matter
what the rest of 'someval' looks like. Isn't that the whole purpose
of testing a bit?

Does the standard say that i am right or should i have written?

if( someval & ab != 0 )
{
// do this
}

Is my compiler wrong in accepting this?

No. The behaviours of

if (integral_expression)

and

if (integral_expression != 0)

My second question, is, if i have a structure
typedef struct
{
char a
int b
}MYSTRUCT *PMYSTRUCT

Why is this dance around the bush? It would be much more C++ to
write

struct MYSTRUCT
{
char a;
int b;
};

typedef MYSTRUCT *PMYSTRUCT;

and i Read(..) a file using sizeof( MYSTRUCT ) will it make a

if

i had declared my structure as
typedef struct
{
int b
char a
}MYSTRUCT *PMYSTRUCT

and what about a structure like
typedef struct
{
int b
char a
ANOTHERSTRUCT * B
}MYSTRUCT *PMYSTRUCT

Yes, it will.