使用std :: shared_ptr对象实例创建boost :: thread

Question

我有以下两个代码段。第一个模块按预期进行编译和工作。但是第二个块不能编译。

我的问题是，给出下面的代码当尝试基于由shared_ptr代理的对象的实例创建线程时，正确的语法是什么？

#include <iostream> 
#include <new> 
#include <memory> 

#include <boost/thread.hpp> 

struct foo 
{ 
    void boo() {} 
}; 

int main() 
{ 
    //This works 
    { 
     foo* fptr = new foo; 
     boost::thread t(&foo::boo,fptr); 
     t.join(); 
     delete fptr; 
    } 

    //This doesn't work 
    { 
     std::shared_ptr<foo> fptr(new foo); 
     boost::thread t(&foo::boo,fptr); 
     t.join(); 
    } 

    return 0; 
} 

编译器错误：

Error 5 error C2784: 'T *boost::get_pointer(T *)' : could not deduce template argument for 'T *' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 3 error C2784: 'T *boost::get_pointer(const std::auto_ptr<_Ty> &)' : could not deduce template argument for 'const std::auto_ptr<_Ty> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 4 error C2784: 'T *boost::get_pointer(const std::auto_ptr<_Ty> &)' : could not deduce template argument for 'const std::auto_ptr<_Ty> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 8 error C2784: 'T *boost::get_pointer(const boost::shared_ptr<X> &)' : could not deduce template argument for 'const boost::shared_ptr<X> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 9 error C2784: 'T *boost::get_pointer(const boost::shared_ptr<X> &)' : could not deduce template argument for 'const boost::shared_ptr<X> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 1 error C2784: 'T *boost::get_pointer(const boost::scoped_ptr<T> &)' : could not deduce template argument for 'const boost::scoped_ptr<T> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 2 error C2784: 'T *boost::get_pointer(const boost::scoped_ptr<T> &)' : could not deduce template argument for 'const boost::scoped_ptr<T> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 6 error C2784: 'T *boost::get_pointer(const boost::reference_wrapper<T> &)' : could not deduce template argument for 'const boost::reference_wrapper<T> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 7 error C2784: 'T *boost::get_pointer(const boost::reference_wrapper<T> &)' : could not deduce template argument for 'const boost::reference_wrapper<T> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 10 error C2784: 'T *boost::get_pointer(const boost::intrusive_ptr<T> &)' : could not deduce template argument for 'const boost::intrusive_ptr<T> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 
Error 11 error C2784: 'T *boost::get_pointer(const boost::intrusive_ptr<T> &)' : could not deduce template argument for 'const boost::intrusive_ptr<T> &' from 'std::tr1::shared_ptr<_Ty>' c:\program files (x86)\boost\boost_1_47\boost\bind\mem_fn_template.hpp 40 1 htest 

Answer 1

的问题是，boost::thread依靠boost::mem_fn处理成员函数和boost::mem_fn（或者至少你正在使用的版本）不知道如何使用一个std::shared_ptr来调用一个成员函数，因为它期望您在错误列表中使用boost::shared_ptr或无数其他智能指针类型之一。

原始指针的工作原理是因为boost::mem_fn已经具有该过载。解决方案是使用boost::shared_ptr或std::mem_fn。后者的作品，因为std::mem_fn知道如何（<boost/mem_fn.hpp>前被包括在内）与std::shared_ptr

boost::thread t(std::mem_fn(&foo::boo), fptr);

Answer 2

戴夫小号的答案另一种方法是定义这个互动：

namespace boost 
{ 
    template<typename T> 
    inline T* 
    get_pointer(const std::shared_ptr<T>& p) 
    { return p.get(); } 
} 

那“教导” boost::mem_fn以获得来自std::shared_ptr的原始指针。

在C++ 11 std::mem_fn需要具有任何指针样型工作，仅通过解除引用它即*fptr，但boost::mem_fn而是使用*boost::get_pointer(fptr)。我不知道它是否已在最新版本的Boost中修复，但我认为它应该使用SFINAE来检测get_pointer是否可以正常工作，并且应该解除引用。