Re: [Boost-users] circular_buffer: rotate() vs erase_begin() for scalars

Subject: Re: [Boost-users] circular_buffer: rotate() vs erase_begin() for scalars
From: Robert Dailey (rcdailey.lists_at_[hidden])
Date: 2017-01-25 10:16:50

On Wed, Jan 25, 2017 at 4:37 AM, Maarten de Vries <maarten_at_[hidden]> wrote:
>
>
> On 24 January 2017 at 16:28, Robert Dailey <rcdailey.lists_at_[hidden]> wrote:
>>
>> On Wed, Jan 18, 2017 at 12:00 PM, Robert Dailey
>> <rcdailey.lists_at_[hidden]> wrote:
>> > I'm using circular_buffer to represent a FIFO queue of bytes:
>> >
>> > boost::circular_buffer<std::uint8_t> m_queue;
>> >
>> > When I read bytes from the "front", I simply do:
>> >
>> > m_queue.erase_begin(num_read_bytes);
>> >
>> > I do so because the documentation for erase_begin() specifically
>> > mentions constant time performance for scalar types since no
>> > destructor needs to be called.
>> >
>> > However, I feel that rotate() better expresses what I'm trying to do.
>> > Is there a reason to prefer one over the other for scalar types?
>>
>> Would it be possible to get some feedback on this?
>
>
> It sounds to me that what you want is erase_begin(). Rotate does not remove
> the
> read bytes but puts them at the end of the sequence. It seems unlikely that
> that is what you want.
>
> That said, rotate is not guaranteed to be constant time. If the circular
> buffer is not full it has to move elements around. The exact time complexity
> can be found in the documentation. Look for "complexity" at
> http://www.boost.org/doc/libs/1_63_0/doc/html/boost/circular_buffer.html#idp47282880-bb

Thank you very much for the response! The boost docs are very
difficult to navigate and understand, so I definitely missed the
details you described. I will continue using erase_begin().