Re: std::vector and a bit-wise copy
On Feb 9, 3:24 pm, Jeremy <bjerem...@yahoo.com> wrote:
I have a question that I having trouble finding a straight answer to,
but thought it may be obvious to someone here.
If I have a struct with a vector as a member:
struct A
{
std::vector<int> theVec;
};
And I make two instances of that vector x and y and populate the
vector in x. Is it undefined behavior to then set y= x ? Such as
int main()
{
A x;
A y;
fill(x); // allocates the vector and populates it
y = x;
}
Seeing A has no copy-constructor declared, we should do a bit-wise
copy from x to y. Since the vector in y has no memory allocated to it,
I'm assuming this should be just a case of memory trampling and
exhibit UB.
Is that wrong or am I missing something w.r.t. the bit-wise copy?
You're wrong because you're missing something wrt the copy.
Per 12.8/13 ([class.copy]):
"The implicitly-defined copy assignment operator for class X performs
memberwise assignemnt of its subobjects."
So it's not a bitwise copy of the vector member, instead
vector<T>::operator=()
is called to copy x.theVec to y.theVec
--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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