Re: vector of pimpl's / weird behavior
On Sep 28, 9:49 pm, er <erwann.rog...@gmail.com> wrote:
the code below generates the following behavior. cld someone please
help understand it?
1) clean project + build project generates build errors (see bottom)
2) build a second time, errors disappears, run: ok
3) uncomment [1] and comment [2], no problem
4) uncomment [3] and [4], also no problem
#ifndef A_IMPL_H_
#define A_IMPL_H_
#include <memory>
class A_impl{
public:
A_impl();
virtual ~A_impl(){};
virtual std::auto_ptr<A_impl> clone()const=0;
private:
A_impl& operator=(const A_impl&);};
#endif /*A_IMPL_H_*/
#ifndef A_H_
#define A_H_
#include <memory>
//#include "A_impl.h" // [1]
class A_impl;//[2]
class A{
public:
A(const A_impl& impl_);
A(const A& o);
A& operator=(const A& rhs);
private:
A();
std::auto_ptr<A_impl> pimpl;};
#endif /*A_H_*/
The line with std::auto_ptr<> is undefined behavior (with the
code as written). According to the standard, you can only
instantiate a template in the standard library over a completely
defined type.
#ifndef AS_H_
#define AS_H_
#include <vector>
#include "A.h"
class As{
public:
As(
const std::vector<A>& sub_collec_
);
private:
std::vector<A> sub_collec;//[3]};
#endif /*AS_H_*/
#include "A.h"
#include "A_impl.h"
A::A(const A_impl& impl_):pimpl(impl_.clone()){};
A::A(const A& o):pimpl((o.pimpl)->clone()){};
A& A::operator=(const A& rhs){
if(&rhs!=this){
pimpl=rhs.pimpl->clone();
};
return *this;};
#include "As.h"
As::As(
const std::vector<A>& sub_collec_
): sub_collec(sub_collec_){};//[4]
instantiated from 'void std::_Destroy(_Tp*) [with _Tp = A]'
testing_vector_pimpl A.h line 6 1191008360119 128231
/usr/lib/gcc/x86_64-linux-gnu/4.1.2/../../../../include/c++/4.1.2/bits/
stl_construct.h instantiated from 'void
std::__destroy_aux(_ForwardIterator, _ForwardIterator, __false_type)
[with _ForwardIterator = A*]' testing_vector_pimpl line 122
1191008360120 128232
/usr/lib/gcc/x86_64-linux-gnu/4.1.2/../../../../include/c++/4.1.2/bits/
stl_construct.h instantiated from 'void
std::_Destroy(_ForwardIterator, _ForwardIterator, std::allocator<_T2>)
[with _ForwardIterator = A*, _Tp = A]' testing_vector_pimpl =
line 182
1191008360120 128234
/usr/lib/gcc/x86_64-linux-gnu/4.1.2/../../../../include/c++/4.1.2/bits/
stl_construct.h instantiated from 'void
std::_Destroy(_ForwardIterator, _ForwardIterator) [with
_ForwardIterator = A*]' testing_vector_pimpl line 155 =
1191008360120
128233
/usr/lib/gcc/x86_64-linux-gnu/4.1.2/../../../../include/c++/4.1.2/bits/
stl_vector.h instantiated from 'std::vector<_Tp, _Alloc>::~vector()
[with _Tp = A, _Alloc = std::allocator<A>]' testing_vec=
tor_pimpl line
272 1191008360120 128235
I don't know exactly why the rebuild eliminates the error with
g++. With some other compilers, however, template
instantiations are stored in a repository; if the template is
successfully instantiated in another translation unit, then the
rebuild will work.
But it doesn't really matter. You have undefined behavior, and
you should fix it.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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