Re: Am I misusing std::vector?
Maciej Sobczak wrote:
loose AT astron DOT nl wrote:
I was surprised by the output of the program below. From
what I understand from the C++ STL documentation,
vector<T>::resize(N), will create N *newly constructed*
objects of T.
No. resize is defined in terms of insert, which is supposed to
insert the given number of *copies* of the given value.
The problem with your code is that struct A does not properly
define copying operations. The default copy constructor will
perform the shallow copy of all its members, which in your
case will result in all objects pointing to the same integer
value. This is exactly what you see.
You might consider reading "Effective C++" by Scott Meyers,
there's a whole chapter about why and how of defining custom
copy operations for classes that manage their own resources.
Note that the code in the original edition wasn't exception safe
(understandable -- compilers didn't implement exceptions at the
time). Knowing Scott, I'm sure that he has corrected this in
later editions, IF it is possible -- I don't know how much
change editors allow in such cases.
I would still highly recommend the book. But if your edition
doesn't talk about exception safety in this regard, be aware
that there is a whole additional aspect which has to be taken
into account.
--
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