c++ - libc++ 的错误？ future 和 C++11

Question

#include <thread>
#include <future>
#include <iostream>
#include <atomic>
#include <cstdint>

template <typename T>
void consumeFuture(std::future<T>&& fut) {
  fut.get();
}

template <typename T>
void actOnT(std::atomic<T>& at) {
  ++at;
}

int main() {
  std::atomic<uint32_t> a{42};
  consumeFuture(std::async(std::launch::async, &actOnT<uint32_t>, std::ref(a)));
  std::cout << a << "\n";
}

此代码在带有 g++ 4.8.1 的 Ubuntu 13.10 64 位下编译得很好和 libstdc++ , 它无法在与 clang 相同的平台上编译和 libc++因为 libc++显然没有以正确的方式实现所有内容的库。

这是 clang 的 c++ 标准库的错误还是我的代码有问题？

我正在使用 1.0~svn181765-1两者的版本 libc++和 libc++abi来自官方 llvm apt 存储库。

用clang++获得的输出与 libc++ :

In file included from future_1.cpp:1:
In file included from /usr/bin/../include/c++/v1/thread:90:
In file included from /usr/bin/../include/c++/v1/__functional_base:15:
/usr/bin/../include/c++/v1/type_traits:2761:19: error: invalid application of 'sizeof' to an incomplete type 'void'
    static_assert(sizeof(_Tp) > 0, "Type must be complete.");
                  ^~~~~~~~~~~
/usr/bin/../include/c++/v1/type_traits:2778:15: note: in instantiation of template class
      'std::__1::__check_complete<void>' requested here
    : private __check_complete<_Rp>
              ^
/usr/bin/../include/c++/v1/type_traits:2947:15: note: in instantiation of template class
      'std::__1::__check_complete<void (*)(std::__1::atomic<unsigned int> &)>' requested here
    : private __check_complete<_Fp>
              ^
/usr/bin/../include/c++/v1/type_traits:2958:11: note: in instantiation of template class
      'std::__1::__invokable_imp<void (*)(std::__1::atomic<unsigned int> &),
      std::__1::reference_wrapper<std::__1::atomic<unsigned int> > >' requested here
          __invokable_imp<_Fp, _Args...>::value>
          ^
/usr/bin/../include/c++/v1/type_traits:2977:30: note: in instantiation of template class 'std::__1::__invokable<void
      (*)(std::__1::atomic<unsigned int> &), std::__1::reference_wrapper<std::__1::atomic<unsigned int> > >' requested
      here
    : public __invoke_of_imp<__invokable<_Fp, _Args...>::value, _Fp, _Args...>
                             ^
/usr/bin/../include/c++/v1/future:2237:17: note: in instantiation of template class 'std::__1::__invoke_of<void
      (*)(std::__1::atomic<unsigned int> &), std::__1::reference_wrapper<std::__1::atomic<unsigned int> > >' requested
      here
future<typename __invoke_of<typename decay<_Fp>::type, typename decay<_Args>::type...>::type>
                ^
future_1.cpp:19:17: note: while substituting deduced template arguments into function template 'async' [with _Fp = void
      (*)(std::__1::atomic<unsigned int> &), _Args = <std::__1::reference_wrapper<std::__1::atomic<unsigned int> >>]
  consumeFuture(std::async(std::launch::async, &actOnT<uint32_t>, std::ref(a)));
                ^
1 error generated.

Answer 1

此版本的 libc++ 修复了此问题: http://llvm.org/viewvc/llvm-project?view=revision&revision=188413