c++ - vector 的 push_back 错误背后的原因是什么

Question

我有一个简单的 C++ std::vector 并且在其中存储线程，如下所示。你能解释一下为什么带有注释“不编译”的行在编译期间显示错误吗？为什么带有注释的行“编译”有效？

#include<thread>
#include<vector>

using namespace std;
void abc() {}
int main()
{
   vector<thread> workers;
   workers.push_back(thread(abc)); // compiles
   thread t(abc);
   workers.push_back(t); // does not compile

   return 0;
 }

更新:我在 Linux 上使用 g++ 4.4.6。下面是错误

[jim@cola c++]$ g++ -std=c++0x -pthread -g -Wall t.cpp -o t
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/x86_64-redhat-linux/bits/c++allocator.h:34,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/allocator.h:48,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/string:43,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/locale_classes.h:42,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ios_base.h:43,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ios:43,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:40,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iostream:40,
                 from t.cpp:1:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/thread: In member function ‘void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, const _Tp&) [with _Tp = std::thread]’:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_vector.h:737:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::thread, _Alloc = std::allocator<std::thread>]’
t.cpp:29:   instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/thread:122: error: deleted function ‘std::thread::thread(const std::thread&)’
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ext/new_allocator.h:105: error: used here
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/vector:69,
                 from t.cpp:4:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/thread: In member function ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, _Args&& ...) [with _Args = const std::thread&, _Tp = std::thread, _Alloc = std::allocator<std::thread>]’:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_vector.h:741:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::thread, _Alloc = std::allocator<std::thread>]’
t.cpp:29:   instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/thread:122: error: deleted function ‘std::thread::thread(const std::thread&)’
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/vector.tcc:314: error: used here

Answer 1

你收到错误是因为 std::thread 是不可复制的， 并且你试图将 t 的拷贝插入到 vector 。

使这项工作成功的唯一方法是:

workers.push_back(std::move(t));

但是，这意味着在您这样做之后，t 不再表示线程(它表示的线程已移入 vector 中)。