Re: vector modifiers and invalidation of iterators
On Jul 26, 9:51 pm, TJorgenson <tjorgen...@infinera.com> wrote:
On Jul 25, 4:12 am, James Kanze <james.ka...@gmail.com> wrote:
To know whether reallocation has happened, we first need
to store the old capacity in a variable; then do the
modification to the vector; then check if the new size is
greater than the variable value (which gives the old
capacity). Is this how we need to check if reallocation
has happened ? In real world applications, how is this
accomplished ? Kindly explain with some sample code.
In real world code, you don't dynamically test; if the
vectors might be invalidated, you just suppose they are, and
get on with it. In real world code, you sometimes to ensure
that they won't be invalidated, e.g. by calling reserve with
a sufficiently large value beforehand.
Agreed, but I still find the OPs question interesting. Is
testing the capacity before and after calling a vector
function that _could_ invalidate iterators a reliable way to
determine if iterators were in fact invalidated by the call?
I mean is this technique guaranteed by the standard?
There's no way to guarantee that the iterators are in fact
invalidated. But if the capacity doesn't change, iterators
pointing to elements before the insertion are guaranteed to not
be invalidated.
Note that you can check this before the insertion as well: if
size() + numberOfElementsToInsert <= capacity(), the insertion
won't invalidate iterators. This could be useful, since before
insertion, you could convert any iterators you had to indexes
(iter - container.begin()), and reconvert the indexes back to
iterators afterwards.
--
James Kanze
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