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I use bitset to save bits of flag. When data is ready, I need to copy
bit values from it to byte buffer. How to do it?

Example.

#include <bitset>
int main()
{
char buffer[32];
std::bitset<256> fcbits;
fcbits.set(1);
fcbits.set(54);
// fcbits -> buffer?
}

Allen

Allen wrote:
> I use bitset to save bits of flag. When data is ready, I need to copy
> bit values from it to byte buffer. How to do it?

By hand.

> Example.
>
> #include <bitset>
> int main()
> {
> char buffer[32];
> std::bitset<256> fcbits;
> fcbits.set(1);
> fcbits.set(54);
> // fcbits -> buffer?
> }

I assume bit n goes to buffer[n/8],bit(n%.
for(int i=0;i<fcbits.size();++i)
{
const int index=n/8;
const char mask=1<<(n%;
if(fcbits[i])buffer[index]|=mask;
else buffer[index]&=~mask;
}

There may be more optimal ways to do it.

--
Michael

Michael DOUBEZ wrote:
> Allen wrote:
>> I use bitset to save bits of flag. When data is ready, I need to copy
>> bit values from it to byte buffer. How to do it?
>
> By hand.
>
>> Example.
>>
>> #include <bitset>
>> int main()
>> {
>> char buffer[32];
>> std::bitset<256> fcbits;
>> fcbits.set(1);
>> fcbits.set(54);
>> // fcbits -> buffer?
>> }
>
> I assume bit n goes to buffer[n/8],bit(n%.
> for(int i=0;i<fcbits.size();++i)
> {
> const int index=n/8;
> const char mask=1<<(n%;
> if(fcbits[i])buffer[index]|=mask;
> else buffer[index]&=~mask;
> }
>
> There may be more optimal ways to do it.
>
if the size allows it, there is also
fcbits.to_ulong()

--
Bertrand

Bertrand wrote:
> Michael DOUBEZ wrote:
>> Allen wrote:
>>> I use bitset to save bits of flag. When data is ready, I need to copy
>>> bit values from it to byte buffer. How to do it?
[snip]
>>> std::bitset<256> fcbits;
[snip]
> if the size allows it, there is also
> fcbits.to_ulong()

With 256 bits, I don't think it will work.

--
Michael

how about reinterpret_cast ?

On Jan 22, 9:05*am, Allen <Allen.Che...@gmail.com> wrote:
> I use bitset to save bits of flag. When data is ready, I need to copy
> bit values from it to byte buffer. How to do it?
>
> Example.
>
> #include <bitset>
> int main()
> {
> * char buffer[32];
> * std::bitset<256> fcbits;
> * fcbits.set(1);
> * fcbits.set(54);
> * // fcbits -> buffer?
>
> }
>
> Allen

Allen <> writes:

> I use bitset to save bits of flag. When data is ready, I need to copy
> bit values from it to byte buffer. How to do it?

Yes, how? How do you want to represent your bits as a string of characters?


> Example.
>
> #include <bitset>
> int main()
> {
> char buffer[32];
> std::bitset<256> fcbits;
> fcbits.set(1);
> fcbits.set(54);
> // fcbits -> buffer?
> }


There's not enough bytes in your buffer.

Surprized? That may be because you don't give a specification precise enough.

Otherwise, why don't you read the reference to the bitset class?
http://www.cplusplus.com/reference/stl/bitset/

--
__Pascal Bourguignon__

Pascal J. Bourguignon wrote:

> Allen <> writes:
>
>> I use bitset to save bits of flag. When data is ready, I need to copy
>> bit values from it to byte buffer. How to do it?
>
> Yes, how? How do you want to represent your bits as a string of
> characters?
>
>
>> Example.
>>
>> #include <bitset>
>> int main()
>> {
>> char buffer[32];
>> std::bitset<256> fcbits;
>> fcbits.set(1);
>> fcbits.set(54);
>> // fcbits -> buffer?
>> }
>
>
> There's not enough bytes in your buffer.

That sounds very definite. How did you tell?

> Surprized? That may be because you don't give a specification precise
> enough.

In that case, I think, all one could say is that for _some_ specifications,
there are not enough bytes in the buffer. For _some_ other specifications,
there are.

> Otherwise, why don't you read the reference to the bitset class?
> http://www.cplusplus.com/reference/stl/bitset/

Or the standard. Now, what particularly is it that the OP should pay
attention to? After all, RTFM is most often not a good answer in a news
group where everything that couldn't be answered that way is off-topic


Best

Kai-Uwe Bux

Kai-Uwe Bux <> writes:

> Pascal J. Bourguignon wrote:
>
>> Allen <> writes:
>>
>>> I use bitset to save bits of flag. When data is ready, I need to copy
>>> bit values from it to byte buffer. How to do it?
>>
>> Yes, how? How do you want to represent your bits as a string of
>> characters?
>>
>>
>>> Example.
>>>
>>> #include <bitset>
>>> int main()
>>> {
>>> char buffer[32];
>>> std::bitset<256> fcbits;
>>> fcbits.set(1);
>>> fcbits.set(54);
>>> // fcbits -> buffer?
>>> }
>>
>>
>> There's not enough bytes in your buffer.
>
> That sounds very definite. How did you tell?
>
>> Surprized? That may be because you don't give a specification precise
>> enough.
>
> In that case, I think, all one could say is that for _some_ specifications,
> there are not enough bytes in the buffer. For _some_ other specifications,
> there are.
>
>> Otherwise, why don't you read the reference to the bitset class?
>> http://www.cplusplus.com/reference/stl/bitset/
>
> Or the standard. Now, what particularly is it that the OP should pay
> attention to? After all, RTFM is most often not a good answer in a news
> group where everything that couldn't be answered that way is off-topic

I would use fcbits.to_string().
In C++, we don't use char[] a lot, we rather use std::string.
bitset::to_string() copies the bit values to a character buffer.
If something else is needed, it must be specified!

--
__Pascal Bourguignon__

Pascal J. Bourguignon wrote:
> Kai-Uwe Bux <> writes:
>
>> Pascal J. Bourguignon wrote:
>>
>>> Allen <> writes:
>>>
>>>> I use bitset to save bits of flag. When data is ready, I need to copy
>>>> bit values from it to byte buffer. How to do it?
>>> Yes, how? How do you want to represent your bits as a string of
>>> characters?
>>>
>>>
>>>> Example.
>>>>
>>>> #include <bitset>
>>>> int main()
>>>> {
>>>> char buffer[32];
>>>> std::bitset<256> fcbits;
>>>> fcbits.set(1);
>>>> fcbits.set(54);
>>>> // fcbits -> buffer?
>>>> }
>>>
>>> There's not enough bytes in your buffer.
>> That sounds very definite. How did you tell?
>>
>>> Surprized? That may be because you don't give a specification precise
>>> enough.
>> In that case, I think, all one could say is that for _some_ specifications,
>> there are not enough bytes in the buffer. For _some_ other specifications,
>> there are.
>>
>>> Otherwise, why don't you read the reference to the bitset class?
>>> http://www.cplusplus.com/reference/stl/bitset/
>> Or the standard. Now, what particularly is it that the OP should pay
>> attention to? After all, RTFM is most often not a good answer in a news
>> group where everything that couldn't be answered that way is off-topic
>
> I would use fcbits.to_string().

In fact you would use to_string<char,char_traits<char>,allocator<char> >().

Which gives you a string of 256 element which is clearly not what the OP
wants since he wants to copy bit values in bit buffer.

> In C++, we don't use char[] a lot, we rather use std::string.

I still use char[] and vector<char> also.

> bitset::to_string() copies the bit values to a character buffer.

It construct a string with a serie of 0 and 1 that represent the values
of the bits which is not the same.

--
Michael

Michael DOUBEZ wrote:
> Bertrand wrote:
>> Michael DOUBEZ wrote:
>>> Allen wrote:
>>>> I use bitset to save bits of flag. When data is ready, I need to copy
>>>> bit values from it to byte buffer. How to do it?
> [snip]
>>>> std::bitset<256> fcbits;
> [snip]
>> if the size allows it, there is also
>> fcbits.to_ulong()
>
> With 256 bits, I don't think it will work.
>
That's why I wrote: *if the size allows it*

--
Bertrand