c ++ 11 std :: async在mingw中不起作用

Question

从Herb Sutter的presentation运行此代码。这在gcc 4.6.3下的linux下工作正常。我认为mingw不支持future.h，但错误很难理解！

#include <iostream>
#include <vector>
#include <string>
#include <future>
#include <algorithm>

using namespace std;

string flip( string s ) {
  reverse( begin(s), end(s) );
  return s;
}

int main() {
  vector<future<string>> v;

  v.push_back( async([]{ return flip(" ,olleH"); }) );
  v.push_back( async([]{ return flip(".gnaL"); }) );
  v.push_back( async([]{ return flip("\n!TXEN"); }) );

  for( auto& e: v ) {
    cout << e.get();
  }
}

这是错误：

$ x86_64-w64-mingw32-g++.exe -std=c++0x -pthread swap.cpp
swap.cpp: In function 'int main()':
swap.cpp:17:51: error: invalid use of incomplete type 'std::__async_sfinae_helper<main()::<lambda()>, main()::<lambda()> >::type {aka class std::future<std::basic_string<char> >}'
In file included from swap.cpp:4:0:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future:111:11: error: declaration of 'std::__async_sfinae_helper<main()::<lambda()>, main()::<lambda()> >::type {aka class std::future<std::basic_string<char> >}'
swap.cpp:18:49: error: invalid use of incomplete type 'std::__async_sfinae_helper<main()::<lambda()>, main()::<lambda()> >::type {aka class std::future<std::basic_string<char> >}'
In file included from swap.cpp:4:0:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future:111:11: error: declaration of 'std::__async_sfinae_helper<main()::<lambda()>, main()::<lambda()> >::type {aka class std::future<std::basic_string<char> >}'
swap.cpp:19:51: error: invalid use of incomplete type 'std::__async_sfinae_helper<main()::<lambda()>, main()::<lambda()> >::type {aka class std::future<std::basic_string<char> >}'
In file included from swap.cpp:4:0:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future:111:11: error: declaration of 'std::__async_sfinae_helper<main()::<lambda()>, main()::<lambda()> >::type {aka class std::future<std::basic_string<char> >}'
swap.cpp:22:14: error: invalid use of incomplete type 'class std::future<std::basic_string<char> >'
In file included from swap.cpp:4:0:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future:111:11: error: declaration of 'class std::future<std::basic_string<char> >'
In file included from c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_algobase.h:68:0,
                 from c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/char_traits.h:41,
                 from c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/ios:41,
                 from c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/ostream:40,
                 from c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/iostream:40,
                 from swap.cpp:1:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_iterator.h: In instantiation of '__gnu_cxx::__normal_iterator<_Iterator, _Container>& __gnu_cxx::__normal_iterator<_Iterator, _Container>::operator++() [with _Iterator = std::future<std::basic_string<char> >*; _Container = std::vector<std::future<std::basic_string<char> > >; __gnu_cxx::__normal_iterator<_Iterator, _Container> = __gnu_cxx::__normal_iterator<std::future<std::basic_string<char> >*, std::vector<std::future<std::basic_string<char> > > >]':
swap.cpp:21:17:   required from here
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_iterator.h:750:2: error: cannot increment a pointer to incomplete type 'std::future<std::basic_string<char> >'
In file included from c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/vector:65:0,
                 from swap.cpp:2:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_vector.h: In instantiation of 'std::_Vector_base<_Tp, _Alloc>::~_Vector_base() [with _Tp = std::future<std::basic_string<char> >; _Alloc = std::allocator<std::future<std::basic_string<char> > >]':
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_vector.h:247:15:   required from 'std::vector<_Tp, _Alloc>::vector() [with _Tp = std::future<std::basic_string<char> >; _Alloc = std::allocator<std::future<std::basic_string<char> > >]'
swap.cpp:15:26:   required from here
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_vector.h:161:9: error: invalid use of incomplete type 'class std::future<std::basic_string<char> >'
In file included from swap.cpp:4:0:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future:111:11: error: declaration of 'class std::future<std::basic_string<char> >'
In file included from c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/vector:63:0,
                 from swap.cpp:2:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_construct.h: In instantiation of 'void std::_Destroy(_ForwardIterator, _ForwardIterator) [with _ForwardIterator = std::future<std::basic_string<char> >*]':
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_construct.h:155:7:   required from 'void std::_Destroy(_ForwardIterator, _ForwardIterator, std::allocator<_T2>&) [with _ForwardIterator = std::future<std::basic_string<char> >*; _Tp = std::future<std::basic_string<char> >]'
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_vector.h:403:9:   required from 'std::vector<_Tp, _Alloc>::~vector() [with _Tp = std::future<std::basic_string<char> >; _Alloc = std::allocator<std::future<std::basic_string<char> > >]'
swap.cpp:15:26:   required from here
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/bits/stl_construct.h:128:7: error: invalid use of incomplete type '_Value_type {aka class std::future<std::basic_string<char> >}'
In file included from swap.cpp:4:0:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future:111:11: error: declaration of '_Value_type {aka class std::future<std::basic_string<char> >}'
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future: At global scope:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future:187:5: error: 'typename std::__async_sfinae_helper<typename std::decay<_Func>::type, _Fn, _Args ...>::type std::async(_Fn&&, _Args&& ...) [with _Fn = main()::<lambda()>; _Args = {}; typename std::__async_sfinae_helper<typename std::decay<_Func>::type, _Fn, _Args ...>::type = std::future<std::basic_string<char> >]', declared using local type 'main()::<lambda()>', is used but never defined [-fpermissive]
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future:187:5: error: 'typename std::__async_sfinae_helper<typename std::decay<_Func>::type, _Fn, _Args ...>::type std::async(_Fn&&, _Args&& ...) [with _Fn = main()::<lambda()>; _Args = {}; typename std::__async_sfinae_helper<typename std::decay<_Func>::type, _Fn, _Args ...>::type = std::future<std::basic_string<char> >]', declared using local type 'main()::<lambda()>', is used but never defined [-fpermissive]
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/include/c++/future:187:5: error: 'typename std::__async_sfinae_helper<typename std::decay<_Func>::type, _Fn, _Args ...>::type std::async(_Fn&&, _Args&& ...) [with _Fn = main()::<lambda()>; _Args = {}; typename std::__async_sfinae_helper<typename std::decay<_Func>::type, _Fn, _Args ...>::type = std::future<std::basic_string<char> >]', declared using local type 'main()::<lambda()>', is used but never defined [-fpermissive]

我在Windows中使用GCC 4.7。

$ g++ -v
Using built-in specs.
COLLECT_GCC=c:\mingw64\bin\x86_64-w64-mingw32-g++.exe
COLLECT_LTO_WRAPPER=c:/mingw64/bin/../libexec/gcc/x86_64-w64-mingw32/4.7.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../gcc-4.7.0/configure --build=x86_64-w64-mingw32 --enable-targets=all --disable-multilib --enable-64bit --prefix=/mingw64 --with-sysroot=/mingw64 --disable-shared --enable-static --disable-nls --enable-version-specific-runtime-libs --disable-win32-registry --without-dwarf2 --enable-sjlj-exceptions --enable-fully-dynamic-string --enable-languages=c,ada,lto,c++,objc,obj-c++,fortran --enable-libgomp --enable-lto --enable-libssp -enable-gnattools --disable-bootstrap --with-gcc --with-gnu-as --with-gnu-ld --with-stabs --enable-interwork --with-mpfr-include=/home/beta/gcc-build/../gcc-4.7.0/mpfr/src --with-mpfr-lib=/home/beta/gcc-build/mpfr/src/.libs
Thread model: win32
gcc version 4.7.0 (GCC)

Answer 1

也许我更容易解释，因为我写了那段代码，但它并不那么难，只要查看错误输出的第一行：

swap.cpp:22:14: error: invalid use of incomplete type 'class std::future<std::basic_string<char> >'

这告诉你std::future是一个不完整的类型，即声明但未定义。下一行告诉您它的确切位置（然后所有其他错误都是由于尝试以不同方式使用该不完整类型而引起的。）

如果查看GCC的<future>标题，您会看到类型在顶部附近声明，但定义依赖于此预处理器条件：

#if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1) \
  && (ATOMIC_INT_LOCK_FREE > 1)

如果您使用这些宏编译一些简单的测试，您会发现_GLIBCXX_HAS_GTHREADS未定义，那是因为您的gcc -v显示了

Thread model: win32

没有人提供必要的代码来使C ++ 11线程功能在Windows上运行。

让<future>工作会更难，但实际上启用<thread>和<mutex>实际上并不困难，但还没有人加紧完成这项工作。昨天我发布了一些关于如何为win32线程模型启用C ++ 11线程功能的想法：http://gcc.gnu.org/ml/libstdc++/2012-05/msg00020.html

Answer 2

名为'MinGW builds'的特殊MinGW构建确实通过gcc提供C ++ 11支持，包括 async ，线程， future 和朋友

（这是IcemanX的低调回答）

已移至http://sourceforge.net/projects/mingwbuilds/

正如Jonathan Wakely指出的那样（正确而权威）其他版本的GCC问题是它们不支持 pthreads ，但是MinGW-build会这样做。使用Windows线程的解决方案可能会更好，但目前无法使用。

我为MinGW build + eclipse 写了详细的安装和设置说明，在这里：http://scrupulousabstractions.tumblr.com/post/36441490955/eclipse-mingw-builds

Answer 3

不知道std :: async是否具有有效的实现（如果有的话），但是std :: thread适用于MinGW / GCC 4.7版本，可在项目站点http://code.google.com/p/mingw-builds/获取

希望这会有所帮助

Answer 4

标准MinGW库＆amp;编译器不支持std::async(*args)

但MinGW的修改版本具有与原版相同的功能，即：TDM-GCC MinGW

免费下载并定期更新。此外，它支持 32＆amp; 64位也用于编译代码。

希望它有所帮助^^

Answer 5

只需从here下载MinGW安装程序，然后使用配置posix线程进行安装。

如果您已经安装了旧的MinGW，请编辑环境变量，以便使用新安装的MinGW。