11

从 Herb Sutter 的演示文稿中运行此代码。这在 gcc 4.6.3 下的 linux 中运行良好。我在想mingw不支持future.h，但是这个错误真的很难理解！

#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)
4

5 回答 5

18

也许对我来说更容易解释，因为我写了那个代码，但这并不难，只要看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> >'

这告诉您这std::future是一个不完整的类型，即它已声明但未定义。下一行会告诉您它的确切声明位置（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。）

如果您查看 GCC 的<future>标头，您会看到类型声明在顶部附近，但是定义取决于此预处理器条件：

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

如果你用这些宏编译一些简单的测试，你会发现_GLIBCXX_HAS_GTHREADS没有定义，那是因为你的gcc -v节目

线程型号：win32

还没有人提供必要的代码来使 C++11 线程功能在 Windows 上运行。

制作<future>工作会更难，但实际上并没有那么难实现<thread>，<mutex>而且还没有人加紧去做这项工作。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

于 2012-05-06T15:56:47.307 回答
3

名为“MinGW builds”的特殊 MinGW 构建确实通过 gcc 提供了 C++11 支持，包括async、thread、future和 friends

（这秒了 IcemanX 否决的答案）

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

正如 Jonathan Wakely 指出的那样（正确且权威地）其他版本的 GCC 的问题是它们不提供对pthreads的支持，但 MinGW-builds 提供。使用 Windows 线程的解决方案可能会更好，但目前不可用。

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

于 2012-12-26T15:04:14.150 回答
2

不知道 std::async 是否有有效的实现（如果有的话），但 std::thread 可与 MinGW/GCC 4.7 版本一起使用，可在项目站点http://code.google.com/p/mingw-builds /

希望这可以帮助

于 2012-04-18T15:23:07.770 回答
0

标准 MinGW 库和编译器不支持std::async(*args)

但是有一个修改版的MinGW，它的功能和原来的一样，就是：TDM-GCC MinGW

它可以免费下载并定期更新。此外，它还支持32 位和 64 位用于编译代码。

希望对你有帮助^^

于 2017-09-14T09:48:00.623 回答
0

只需从此处下载 MinGW 安装程序并使用配置 posix 线程进行安装。

在此处输入图像描述

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

于 2018-07-24T03:01:48.167 回答