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

Jiergir Ogoerg f35f22fan at gmail.com
Sun Dec 29 20:10:53 CET 2013

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 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.

Because QVector doesn't have any of the 2 methods currently I have to
loop thru each my_struct
elements and do each time a memcpy() to a temporary variable and
push_back() it to the QVector.

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