C++ Pass the reference of the class to a vector inside the constructor

Question

Okay so i have an extern vector of pointer type 'Entity', and what i want to do is, when a new Entity type class gets constructed it gets pushed back in the vector of Entities, in C# this would be possible by passing 'this' as a parameter, but i'm unable to do that in c++ ! Here is my code:

'Public.h':

// other code
    #ifndef Entity_h
    #include "Entity.h"
    extern vector <Entity*> AllEntities;
    #endif
// other code

I've put the code in Include guards to not get in trouble, because i'm including 'Public.h' from 'Entity.cpp' and if i didn't have guards it would become a circular dependency !

'Public.cpp':

// other code
#ifndef Entity_h
vector <Entity*> AllEntities;
#endif
// other code

Everything fine, no errors!

'Entity.cpp':

#include "Public.h"
#include "Entity.h"

Entity::Entity()
{
// other code
    AllEntities.push_back(this);
}

i'm trying to do this, but doing this causes me some linker errors:

   Error    3   error LNK2005: "void __cdecl AddToAllENT(class Entity *)" (?AddToAllENT@@YAXPAVEntity@@@Z) already defined in Entity.obj    C:\Users\drin-_000\Documents\Visual Studio 2013\Projects\ECSystem\ECSystem\Public.obj   ECSystem
    Error   4   error LNK2001: unresolved external symbol "class std::vector<class Entity *,class std::allocator<class Entity *> > AllEntities" (?AllEntities@@3V?$vector@PAVEntity@@V?$allocator@PAVEntity@@@std@@@std@@A) C:\Users\drin-_000\Documents\Visual Studio 2013\Projects\ECSystem\ECSystem\Entity.obj   ECSystem
    Error   5   error LNK1120: 1 unresolved externals   C:\Users\drin-_000\Documents\Visual Studio 2013\Projects\ECSystem\Debug\ECSystem.exe    1   1   ECSystem

When i try to do this:

Entity::Entity()
{
// other code
    AllEntities->push_back(this);
}

it gives me these errors!

Error   1   error C2819: type 'std::vector<Entity *,std::allocator<_Ty>>' does not have an overloaded member 'operator ->'  c:\users\drin-_000\documents\visual studio 2013\projects\ecsystem\ecsystem\entity.cpp   9   1   ECSystem
Error   2   error C2232: '->std::vector<Entity *,std::allocator<_Ty>>::push_back' : left operand has 'class' type, use '.'  c:\users\drin-_000\documents\visual studio 2013\projects\ecsystem\ecsystem\entity.cpp   9   1   ECSystem
    3   IntelliSense: expression must have pointer type c:\Users\drin-_000\Documents\Visual Studio 2013\Projects\ECSystem\ECSystem\Entity.cpp   9   2   ECSystem

Answer 1

Eventually i fixed this, by removing the include guards in 'Public.cpp', they were unnecessary because i already put them inside 'Public.h', and they were causing the errors !