How to forward declare vector* (not vector or vector)?

Question

I know we can insulate a class by using pointer so that the header of the class is not required in header, e.g.:

class B;
class A{
    B* b;
};

It prevents #include "B.h" in A.h. Now I want to prevent

#include <vector>

in header, so I try to copy the syntax, use a pointer of vector:

class std::vector<B*>;
class A{
    std::vector<B*>* v;
};

but it failed to compile, is it possible to prevent include vector header by using pointer of vector?

The purpose of forward declarations is to reduce compilation time. When a header changes, there is less to compile. The definition of vector isn't going to change often, so just include the header — Jared Dykstra, Nov 24 '15 at 02:52
@JaredDykstra you are allowed to add explicit specializations of existing functions in `namespace std` — M.M, Nov 24 '15 at 02:56

score 3 · Answer 1 · edited May 23 '17 at 12:14

3

You're looking for:

#include <vector>

class B;
class A
{
    std::vector<B *> *v;
};

It's not permitted to attempt to provide your own declarations for members of namespace std;

If you do not want your header to include <vector> then you cannot use any type involving vector in your class. You could use a pImpl instead.

edited May 23 '17 at 12:14

Community

answered Nov 24 '15 at 02:55

M.M

score 0 · Answer 2 · answered Nov 24 '15 at 02:56

0

No need of doing class std::vector; define class A as

#include <vector>
class B;
class A
{
  std::vector<B*> *v; 
};

Or you can typedef std::vector<B*> VEC_PTR_B_T; and use VEC_PTR_B_T *v in class A.

answered Nov 24 '15 at 02:56

SEB

2 Answers2