Efficiently creating a vector<char> which is a copy of a char[]

[Steven Reddie]

I have a large char[] which I'd like to copy a portion of into a
vector<char>. I can't seem to locate a simple method for doing so. I
assume involving iterators will not result in memcpy not being used
and therefore will be less than optimal. Can anyone help me out?

Regards,

Steven

[Alf P. Steinbach]

Re: Efficiently creating a vector&lt;char& gt; which is a copy of a char[]

On 5 Feb 2004 21:28:39 -0800, smr@essemer.com .au (Steven Reddie) wrote:
[color=blue]
>I have a large char[] which I'd like to copy a portion of into a
>vector<char> . I can't seem to locate a simple method for doing so. I
>assume involving iterators will not result in memcpy not being used
>and therefore will be less than optimal. Can anyone help me out?[/color]

Check the std::vector constructors for constructing a vector from a
character array.

Check the resizing member functions and std::copy for copying into
an existing vector.

[Jonathan Turkanis]

Re: Efficiently creating a vector&lt;char& gt; which is a copy of a char[]

"Steven Reddie" <smr@essemer.co m.au> wrote in message
news:f93791bd.0 402052128.5582a 02a@posting.goo gle.com...[color=blue]
> I have a large char[] which I'd like to copy a portion of into a
> vector<char>. I can't seem to locate a simple method for doing so.[/color]
I[color=blue]
> assume involving iterators will not result in memcpy not being used
> and therefore will be less than optimal. Can anyone help me out?
>[/color]

A good implementation of std::copy will use memcpy, memmove or
something similar in the case you describe. You could also use
char_traits<cha r>::copy.

Jonathan

[tom_usenet]

Re: Efficiently creating a vector&lt;char& gt; which is a copy of a char[]

On 5 Feb 2004 21:28:39 -0800, smr@essemer.com .au (Steven Reddie)
wrote:
[color=blue]
>I have a large char[] which I'd like to copy a portion of into a
>vector<char> . I can't seem to locate a simple method for doing so. I
>assume involving iterators will not result in memcpy not being used
>and therefore will be less than optimal. Can anyone help me out?[/color]

std::vector<cha r> v(chararray, chararray + sizeof(chararra y));

will collapse to a memcpy or memmove call on most (all?) vector
implementations I know of. Trace in with a debugger to confirm.

Tom

C++ FAQ: http://www.parashift.com/c++-faq-lite/
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html

[Steven Reddie]

Re: Efficiently creating a vector&lt;char& gt; which is a copy of a char[]

tom_usenet <tom_usenet@hot mail.com> wrote in message news:<gku620hmh p57gqc1m88kt4ov b40h2lsvr8@4ax. com>...[color=blue]
> On 5 Feb 2004 21:28:39 -0800, smr@essemer.com .au (Steven Reddie)
> wrote:
>
> std::vector<cha r> v(chararray, chararray + sizeof(chararra y));
>
> will collapse to a memcpy or memmove call on most (all?) vector
> implementations I know of. Trace in with a debugger to confirm.[/color]

Thanks guys. It looks like I'm misreading the docs. This last form
of constructor must be the one defined as:

template<class InputIterator> vector(InputIte rator _First,
InputIterator _Last);

which implies that InputIterator for a vector<char> is or is
implicitly constructed from a char*. It's been a while since I've
used the STL that it seems that I'm forgetting some really basic
stuff.

Regards,

Steven

[tom_usenet]

Re: Efficiently creating a vector&lt;char& gt; which is a copy of a char[]

On 6 Feb 2004 19:14:52 -0800, smr@essemer.com .au (Steven Reddie)
wrote:
[color=blue]
>tom_usenet <tom_usenet@hot mail.com> wrote in message news:<gku620hmh p57gqc1m88kt4ov b40h2lsvr8@4ax. com>...[color=green]
>> On 5 Feb 2004 21:28:39 -0800, smr@essemer.com .au (Steven Reddie)
>> wrote:
>>
>> std::vector<cha r> v(chararray, chararray + sizeof(chararra y));
>>
>> will collapse to a memcpy or memmove call on most (all?) vector
>> implementations I know of. Trace in with a debugger to confirm.[/color]
>
>Thanks guys. It looks like I'm misreading the docs. This last form
>of constructor must be the one defined as:
>
>template<cla ss InputIterator> vector(InputIte rator _First,
>InputIterato r _Last);
>
>which implies that InputIterator for a vector<char> is or is
>implicitly constructed from a char*.[/color]

That constructor is the one that matches. You end up calling:

vector<char>::v ector<char*>(ch ar* _First, char* _Last);

That templated constructor should dispatch to a memmove/memcpy
implementation, since char is a scalar and char* is a simple pointer
or the same type.

Tom

C++ FAQ: http://www.parashift.com/c++-faq-lite/
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html