C++ static vs non static class members

Question

I have a class, let's call it Foo Foo does not compile when I include the following line in the class in the header.

static std::vector<UnvalidatedSocket*> unvalidatedSockets;

and the following line in the cpp.

            Foo::unvalidatedSockets.push_back(new UnvalidatedSocket(ClientSocket));

when I take the statickeyword away it compiles just fine. I checked for circular includes but there are none.

The error is LNK2001, unresolved external symbol

Why does this happen? Do static class members get included earlyer on?

static members need to be initialized not only declared. Add `std::vector Foo::unvalidatedSocket;` to your cpp file. — Quest, Oct 11 '16 at 20:05
Do not tell anybody what error you are getting, that would be much more interesting for people to guess... — Slava, Oct 11 '16 at 20:09
Darnit.. I really don't like that you have to double declare stuff in c++. (Well, not really double declare.) Seems that there is still stuff a javadevelopper can learn — blipman17, Oct 11 '16 at 20:09
@blipman17 I really do not like when people do not ask questions properly, for example telling about errors and not showing them, calling linker errors "it does not compile" etc — Slava, Oct 11 '16 at 20:13
dumb error from me, Added the error to the description of the problem. — blipman17, Oct 11 '16 at 20:15

Brick · Accepted Answer · 2016-10-11T20:10:20.703

1

You need to initialize your static member somewhere in the CPP file before you try to push something onto it. Add something like this:

std::vector<UnvalidatedSocket*> Foo::unvalidatedSockets;

edited Oct 11 '16 at 20:10

answered Oct 11 '16 at 20:05

Brick

Have you tried to compile this? – Slava Oct 11 '16 at 20:08
No need for `= std::vector()`, it will be default constructed automatically. Never mind the fact that it's incomplete. – Mark Ransom Oct 11 '16 at 20:08
@Slava Of course I have none of the OP's code, so there's nothing for me to compile... If the syntax is off, I'll be happy to correct it. – Brick Oct 11 '16 at 20:09
@Brick how do you expect this `std::vector();` to compile? – Slava Oct 11 '16 at 20:10
I'm trying to compile it right now. – blipman17 Oct 11 '16 at 20:11
It compiles, runs... perfect! – blipman17 Oct 11 '16 at 20:12
Dumb fact, I had this exact same problem earlyer but didn't recognise that that was actually thesame problem. – blipman17 Oct 11 '16 at 20:13

1 Answers1