std：：async([](){ std：：cout<< "Hello " ; }) build error

std::async([](){ std::cout<< "Hello "; }) build error

本文关键字：std lt error build Hello cout async      更新时间：2023-10-16

CppCon 2015： Detlef Vollmann "Executors for C++ - A Long Story ..."从这个例子开始：

std::async([](){ std::cout << "Hello "; });
std::async([](){ std::cout << "World!n"; });

C++参考资料显示std::async在<future>中，std::cout在<iostream>中。使构建工作缺少什么？

$ cat >hw.cpp <<EOF
> #include <iostream>
> int main(){
>     std::cout << "Hello World!n";
> }
> EOF
$ clang++ -std=c++14 hw.cpp
$ ./a.out
Hello World!
$ cat >cppcon15.cpp <<EOF
> #include <future>
> #include <iostream>
> int main(){
>     std::async([](){ std::cout << "Hello "; });
>     std::async([](){ std::cout << "World!n"; });
> }
> EOF
$ clang++ -std=c++14 cppcon15.cpp
/tmp/cppcon15-4f0a58.o: In function `std::thread::thread<std::__future_base::_Async_state_impl<std::_Bind_simple<main::$_1 ()>, void>::_Async_state_impl(std::_Bind_simple<main::$_1 ()>&&)::{lambda()#1}>(std::__future_base::_Async_state_impl<std::_Bind_simple<main::$_1 ()>, void>::_Async_state_impl(std::_Bind_simple<main::$_1 ()>&&)::{lambda()#1}&&)':
cppcon15.cpp:(.text+0x2cf6): undefined reference to `pthread_create'
/tmp/cppcon15-4f0a58.o: In function `std::thread::thread<std::__future_base::_Async_state_impl<std::_Bind_simple<main::$_0 ()>, void>::_Async_state_impl(std::_Bind_simple<main::$_0 ()>&&)::{lambda()#1}>(std::__future_base::_Async_state_impl<std::_Bind_simple<main::$_0 ()>, void>::_Async_state_impl(std::_Bind_simple<main::$_0 ()>&&)::{lambda()#1}&&)':
cppcon15.cpp:(.text+0x6bb6): undefined reference to `pthread_create'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
您需要使用

-pthread 进行编译，以便链接器允许您使用异步/未来/线程功能。

对于许多库，您必须在链接时包含对库的引用。对于<future>，我相信这是--pthread。

所以试试，clang++ --std=c++14 cppcon15.cpp --pthread.

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