Insert into vector having objects without copy constructor

Question

I have a class whose copy constructors are explicitly deleted (because A uses pointers internally and I don't want to fall into shallow copy pitfalls):

class A {   public:     A(const A&) = delete;     A& operator=(const A&) = delete;      A(const B& b, const C& c); } 

Now I have a vector of type vector<A> aVector; and I want to insert elements into it - so I use emplace_back:

aVector.emplace_back(b, c); 

However, this fails to compile using gcc and I get the error -

third-party/gcc-4.7.1-glibc-2.14.1/libgcc/libgcc-4.7.1/afc21dc/include/c++/4.7.1/bits/stl_construct.h: In instantiation of 'void std::_Construct(_T1*, _Args&& ...) third-party/gcc-4.7.1-glibc-2.14.1/libgcc/libgcc-4.7.1/afc21dc/include/c++/4.7.1/bits/stl_uninitialized.h:77:3:   required from 'static _ForwardIterator std::__uninitialized_copy<_TrivialValueTypes>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator)   third-party/gcc-4.7.1-glibc-2.14.1/libgcc/libgcc-4.7.1/afc21dc/include/c++/4.7.1/bits/stl_uninitialized.h:119:41:   required from '_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator)  third-party/gcc-4.7.1-glibc-2.14.1/libgcc/libgcc-4.7.1/afc21dc/include/c++/4.7.1/bits/stl_uninitialized.h:260:63:   required from '_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&)  third-party/gcc-4.7.1-glibc-2.14.1/libgcc/libgcc-4.7.1/afc21dc/include/c++/4.7.1/bits/stl_uninitialized.h:283:67:   required from '_ForwardIterator std::__uninitialized_move_if_noexcept_a(_InputIterator, _InputIterator, _ForwardIterator, _Allocator&) third-party/gcc-4.7.1-glibc-2.14.1/libgcc/libgcc-4.7.1/afc21dc/include/c++/4.7.1/bits/vector.tcc:410:6:   required from 'void std::vector<_Tp, _Alloc>::_M_emplace_back_aux(_Args&& ...)  third-party/gcc-4.7.1-glibc-2.14.1/libgcc/libgcc-4.7.1/afc21dc/include/c++/4.7.1/bits/vector.tcc:102:4:   required from 'void std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) 

What is the reason for this error and how can it be fixed without removing the deletion of the copy constructors? Do I need a move constructor - does it need to be explicitly defined?

Answer 1

You should add move constructor - because std::vector::emplace_back may do relocation which requires copy/move constructor. Or just use std::deque.

LIVE DEMO

#include <vector> #include <deque> using namespace std;  struct NoCopyNoMove {     NoCopyNoMove(const NoCopyNoMove&) = delete;     NoCopyNoMove& operator=(const NoCopyNoMove&) = delete;     NoCopyNoMove(NoCopyNoMove&&) = delete;     NoCopyNoMove& operator=(NoCopyNoMove&&) = delete;      NoCopyNoMove(int){}; };  struct OnlyMove {     OnlyMove(const OnlyMove&) = delete;     OnlyMove& operator=(const OnlyMove&) = delete;     OnlyMove(OnlyMove&&) noexcept {}     OnlyMove& operator=(OnlyMove&&) noexcept {}      OnlyMove(int){}; };  int main() {     deque<NoCopyNoMove> x;     x.emplace_back(1);      vector<OnlyMove> y;     y.emplace_back(1); } 

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§ 23.2.3 Table 101 — Optional sequence container operations

a.emplace_back(args) [...]

Requires: T shall be EmplaceConstructible into X from args. For vector, T shall also be MoveInsertable into X.