[Development] OK to add zero/bulk copy to QVector?

Giuseppe D'Angelo dangelog at gmail.com
Sun Dec 29 22:28:25 CET 2013

On Sun, Dec 29, 2013 at 8:10 PM, Jiergir Ogoerg <f35f22fan at gmail.com> wrote:
> Hi,
> there are 2 simple options to speed up setting/adding elements to a
> vector when a heap buffer is filled in in advance:
> 1) Bulk copy.
> Assign a bunch of elements at once (from another vector or array),
> like std::vector::assign() does.
> A big extra copy happens, but avoids multiple calls to push_back().
> 2) Zero copy.
> Set the buffer of the (Q)Vector directly along with the number of
> elements to bypass any copying whatsoever, std::vector lacks this
> apparently.
> Apparently QVector lacks both. Would it be OK adding any or both of them?
> Case in point. I got a buffer on the heap:
> my_struct *arr = new my_struct[count];
> Then the arr is filled in from a file or another source, then I could
> do a direct assignment without any copy and multiple callbacks to
> push_back(), let's call this method setBuffer(void *buf, elem_count):
> qtvec->setBuffer(arr, count);
> obviously no need to call delete[] arr after this.

But... is this your *real* code? Can't you instead do

QVector<my_struct> v(count);
fillFromFile(v.data(), count);

or use std::copy or similar?
Giuseppe D'Angelo

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