将ofstream传递给线程函数 [英] Passing an ofstream to a thread function

问题描述

我一直在查看线程，并在尝试将对ofstream的引用传递给线程函数时遇到错误:

I've been looking at threads and have run into an error when I try to pass a reference to an ofstream to the thread function:

这是代码:

void threader(ofstream& fsOutputFileStream)
{ 
    fsOutputFileStream << "hello";
} 
int main() 
{

  ofstream fsOutputFileStream;
  fsOutputFileStream.open("afile.txt", ios::out);

  thread t(threader, fsOutputFileStream);
  thread u(threader, fsOutputFileStream);
  t.join(); 
  u.join();
} 

当我尝试编译时，出现此错误:

When I try to compile I get this error:

threadtest.cpp:18: error:   initializing argument 2 of âboost::thread::thread(F, A1) [with F = void (*)(std::ofstream&), A1 = std::basic_ofstream<char, std::char_traits<char> >]â

如果我将线程位取出并正常地将引用传递给函数，就没有问题. 任何帮助表示赞赏. 谢谢

If I take the threading bits out and just pass the reference to the function normally there is no problem. Any help appreciated. Thanks

推荐答案

未经测试，但尝试std::ref.

rationale :thread构造函数使用可变参数模板来转发参数；如果此处未启用完美转发 ¹ ，则需要将引用包装起来，这样它就不会按值传递).

rationale: thread constructor uses variadic templates to forward the arguments; if perfect forwarding is not enabled there¹, you'll need to wrap the reference so it doesn't get passed by value).

void threader(ofstream& fsOutputFileStream)
{ 
    fsOutputFileStream << "hello";
} 
int main() 
{

  ofstream fsOutputFileStream;
  fsOutputFileStream.open("afile.txt", ios::out);

  thread t(threader, std::ref(fsOutputFileStream));
  thread u(threader, std::ref(fsOutputFileStream));
  t.join(); 
  u.join();
} 

P.S.考虑为输出流添加同步...

P.S. Consider adding synchronization for the output stream...

¹ 完美的转发需要打包扩展，例如std::forward<Args>(arguments)... ;它可能尚未在您的编译器上实现，或它可能未被设计使用(以防止在线程之间意外共享数据)

¹ perfect forwarding requires a pack expansion like std::forward<Args>(arguments)...; It might not yet be implemented on your compiler, or it might not be used by design (to prevent accidentally sharing data between threads)

这篇关于将ofstream传递给线程函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！