Auto pointer (smart) in vector

Question

I am having trouble in solving the below code. I understand auto_ptr cannot be used in STL due to the copy issue. But I am not able to solve this using the C++11 unique_ptr as well. Can you please help me solve this?

Error:

    $ g++ -std=c++0x autoinvec.cpp
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/unique_ptr.h: In copy constructor âvna_data::vna_data(const vna_data&)â:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/unique_ptr.h:214: error: deleted function âstd::unique_ptr<_Tp, _Tp_Deleter>::unique_ptr(const std::unique_ptr<_Tp, _Tp_Deleter>&) [with _Tp = MyClass, _Tp_Deleter = std::default_delete<MyClass>]â
autoinvec.cpp:11: error: used here
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/unique_ptr.h:214: error: deleted function âstd::unique_ptr<_Tp, _Tp_Deleter>::unique_ptr(const std::unique_ptr<_Tp, _Tp_Deleter>&) [with _Tp = MyClass, _Tp_Deleter = std::default_delete<MyClass>]â
autoinvec.cpp:11: error: used here
autoinvec.cpp: In function âint main()â:
autoinvec.cpp:39: note: synthesized method âvna_data::vna_data(const vna_data&)â first required here
autoinvec.cpp:39: error:   initializing argument 1 of âvoid Usethis::pushmydata(VNADATA)â
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/unique_ptr.h: In member function âvna_data& vna_data::operator=(const vna_data&)â:
autoinvec.cpp:11:   instantiated from âvoid std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, _Args&& ...) [with _Args = vna_data, _Tp = vna_data, _Alloc = std::allocator<vna_data>]â
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/vector.tcc:100:   instantiated from âvoid std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = vna_data, _Tp = vna_data, _Alloc = std::allocator<vna_data>]â
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_vector.h:747:   instantiated from âvoid std::vector<_Tp, _Alloc>::push_back(_Tp&&) [with _Tp = vna_data, _Alloc = std::allocator<vna_data>]â
autoinvec.cpp:27:   instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/unique_ptr.h:219: error: deleted function âstd::unique_ptr<_Tp, _Tp_Deleter>& std::unique_ptr<_Tp, _Tp_Deleter>::operator=(const std::unique_ptr<_Tp, _Tp_Deleter>&) [with _Tp = MyClass, _Tp_Deleter = std::default_delete<MyClass>]â
autoinvec.cpp:11: error: used here
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/unique_ptr.h:219: error: deleted function âstd::unique_ptr<_Tp, _Tp_Deleter>& std::unique_ptr<_Tp, _Tp_Deleter>::operator=(const std::unique_ptr<_Tp, _Tp_Deleter>&) [with _Tp = MyClass, _Tp_Deleter = std::default_delete<MyClass>]â
autoinvec.cpp:11: error: used here
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/vector:69,
                 from autoinvec.cpp:3:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/vector.tcc: In member function âvoid std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, _Args&& ...) [with _Args = vna_data, _Tp = vna_data, _Alloc = std::allocator<vna_data>]â:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/vector.tcc:314: note: synthesized method âvna_data& vna_data::operator=(const vna_data&)â first required here

Code:

#include<iostream>
#include<memory>
#include<vector>
using namespace std;

class MyClass {
public:
 MyClass() { cout << "Myclass const" << endl; }
};

typedef struct vna_data {
 string i;
 auto_ptr<MyClass> ap1;
 auto_ptr<MyClass> ap2;
 string j;
 string m;
} VNADATA;

class Usethis {
 vector<VNADATA> _data;
public:
 Usethis() {cout << "Usethis const" << endl; }
 void pushmydata (VNADATA d);
};

void Usethis::pushmydata(VNADATA d) {
 _data.push_back(d);
}

int main () {

 Usethis u;
 VNADATA da;
 da.i = "one";
 da.j = "two";
 da.m = "three";
 da.ap1 = new MyClass();
 da.ap2 = new MyClass();
 u.pushmydata(da);

 return 0;
}

Code with Unique_ptr:

#include<iostream>
#include<memory>
#include<vector>
using namespace std;

class MyClass {
public:
 MyClass() { cout << "Myclass const" << endl; }
};

typedef struct vna_data {
 string i;
 unique_ptr<MyClass> ap1;
 unique_ptr<MyClass> ap2;
 string j;
 string m;
} VNADATA;

class Usethis {
 vector<VNADATA> _data;
public:
 Usethis() {cout << "Usethis const" << endl; }
 void pushmydata (VNADATA d);
};

void Usethis::pushmydata(VNADATA d) {
 _data.push_back(move(d));
}

int main () {

 Usethis u;
 VNADATA da;
 da.i = "one";
 da.j = "two";
 da.m = "three";
 da.ap1.reset( new MyClass );
 da.ap2.reset( new MyClass );
 u.pushmydata(da);

 return 0;
}

Answer 1

Your last line:

u.pushmydata(da);

would require copy. You shall use move here just as you did earlier:

u.pushmydata(std::move(da));

and it makes the code compile.

Answer 2

unique_ptr is moveable but not copyable. Your Usethis::pushmydata method takes a VNADATA by value, which tries to copy the unique_ptr, so it breaks.

The compiler points you to the use of the pushmydata method on line 39:

autoinvec.cpp: In function int main():
autoinvec.cpp:39: note: synthesized method vna_data::vna_data(const vna_data&) first required here
autoinvec.cpp:39: error:   initializing argument 1 of void Usethis::pushmydata(VNADATA)

To fix your problem, change the signature of Usethis::pushmydata to;

void Usethis::pushmydata(VNADATA&& d)

Answer 3

I think you will make your life easier if you use std::shared_ptr and std::make_shared.

#include<iostream>
#include<memory>
#include<vector>
using namespace std;

class MyClass {
public:
 MyClass() { cout << "Myclass const" << endl; }
};

typedef struct vna_data {
 string i;
 shared_ptr<MyClass> ap1;
 shared_ptr<MyClass> ap2;
 string j;
 string m;
 vna_data(shared_ptr<MyClass> ap1, shared_ptr<MyClass> ap2) : ap1(ap1), ap2(ap2) {

 }
} VNADATA;

class Usethis {
 vector<VNADATA> _data;
public:
 Usethis() {cout << "Usethis const" << endl; }
 void pushmydata (VNADATA d);
};

void Usethis::pushmydata(VNADATA d) {
 _data.push_back(d);
}

int main () {

 Usethis u;
 VNADATA da(std::make_shared<MyClass>(), std::make_shared<MyClass>());
 da.i = "one";
 da.j = "two";
 da.m = "three";
 u.pushmydata(da);
}