C / C++ / MFC Discussion Boards

How to overload [] and = for bit assignment

ICantChangeMyAcct14-Jun-04 15:48

14-Jun-04 15:48

I have the following class:

template<typename FLAGTYPE> // may be BYTE, WORD, ULONG...
class Flags {
public:
/**
The boolean indexing operator returns true if the indexed flag bit
is a one.
*/
bool operator[] (long ix) const
{
assert((long)ix >= 0 && (long)ix < 8*sizeof(FLAGTYPE));
return ((m_flags & (1<<ix)) != 0);
}

// ...

protected:
FLAGTYPE m_flags;
};

The bool operator[] makes it possible to write:

Flags<ULONG> f1 = 10;
bool b = f1[3]; // assigns bit 3 of f1, i.e. f1 & 0x08, to b

How do I define indexing and assignment operators that *set* bit 'ix' to a boolean value, so that I can write:

f1[3] = true;

Re: How to overload [] and = for bit assignment

Michael Dunn14-Jun-04 20:28

Michael Dunn

14-Jun-04 20:28

You can't do that directly because the return value of a function can't be a bitfield. You would need to have operator[] return some object (probably a helper class) that has access to the members of Flags<> variable and an operator= that takes a bool parameter. That operator= would twiddle the right bit.

--Mike--
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Can I use Shell Extentions?

ngocdq14-Jun-04 15:16

ngocdq

14-Jun-04 15:16

- I Want to detect a file which have received from other Computer on LAN. But I don't know way to approach.
--> What's should i do??
--> Can I use Shell Extentions??

thanks

Re: Can I use Shell Extentions?

Iain Clarke, Warrior Programmer14-Jun-04 23:44

Iain Clarke, Warrior Programmer

14-Jun-04 23:44

*How* are you receiving it? If you've fetched it from the other computer, then look at the
application fetching the file.

If it is out of your control, (ie. you have a shared directory, and the other PC pushes the file),
then you may be able to use the FindFirstChangeNotification API function.

Iain.

C++ question.

WREY14-Jun-04 14:37

WREY

14-Jun-04 14:37

I created a structure inside a function definition (which means that the structure will be destroyed when I leave that function scope). While I'm inside that function however, I would like to activate another function (let's call it 'DoSomethingWithStruct') to handle certain activities on that newly created structure.

In the class definition, I am able to get away declaring 'DoSomethingWithStruct' by using a 'void*' as the parameter to pass data between one function and the other.

My problem is, "How do I cast the 'void*' back to the structure when I'm inside 'DoSomethingWithStruct'? (Here's some code.)

class MyClass
{
...
void DoSomethingWithStruct(void* pMyStructure);
};

===============================

void MyClass::FirstFn()
{
struct MyStruct {...};
...
DoSomethingWithStruct(pMyStruct);
...
};

================================

void MyClass::DoSomethingWithStruct(void* pMyStructure)
{
// Here is where I need to cast 'pMyStructure' back from a 'void', to a 'MyStruct' type.
}

================================

I DO NOT want to declare 'MyStruct' as global.

Thanks for any insight.

Smile | :)

William

Fortes in fide et opere!