Clang 4.6.2, use shared_ptr

Question

From PNaCl, I use libstdc++ to compile same code. But I want use shared_ptr and I obtain this error :

error: call to implicitly-deleted copy constructor of

This problem have issue :

Using std::shared_ptr with clang++ and libstdc++

I understand, but I don't know how resolve this. I quote the solution :

Adding a defaulted copy constructor and copy assignment operator to shared_ptr will fix the problem.

I add this in shared_ptr.h:

shared_ptr(const shared_ptr&) noexcept = default;

But compiler returns now this error :

F:/nacl_sdk/pepper_31/toolchain/win_pnacl/usr/include/c++/4.6.2/bits/shared_ptr.
h:268:19: error:
  exception specification of explicitly defaulted copy assignment operator
  does not match the calculated one
  shared_ptr& operator=(const shared_ptr&) noexcept = default;
              ^

In this chain of error, I finish here.

Somebody have tips, please?

Answer 1

I was able to repro your bug with this simple test case:

#include <memory>

int main() {
  std::shared_ptr<int> foo;
  std::shared_ptr<int> bar(foo);
  std::shared_ptr<int> baz;
  baz = foo;
  return 0;
}

Building with pnacl-clang++ -std=c++11 -stdlib=libstdc++ test.cc

The easiest way to fix it it is to use libc++ instead of libstdc++:

pnacl-clang++ -std=c++11 -stdlib=libc++ test.cc

This is "experimental" in pepper_31, but will be the default in pepper_33 and higher (which is currently pepper_canary). See https://groups.google.com/forum/#!topic/native-client-discuss/0spfg6O04FM for more info about this switch.

I was also able to hack two headers to make it work with libstdc++:

In bits/shared_ptr.h:

template<typename _Tp>
class shared_ptr : public __shared_ptr<_Tp>
{
public:
  shared_ptr(const shared_ptr&) = default;
  shared_ptr& operator =(const shared_ptr&) = default;
  ...

In bits/shared_ptr_base.h:

template<typename _Tp, _Lock_policy _Lp>
class __shared_ptr
{
public:
  __shared_ptr(const __shared_ptr&) = default;
  __shared_ptr& operator =(const __shared_ptr&) = default;
  ...

IMO, using libc++ is a better solution here. :)