Error C2248 in MVSE12 with std::thread - c++

Question

Good evening everyone !
I am trying to code a multi-threaded application in C++ with Microsoft Visual Studio Express 2012.
The idea us that the "main" function call a thread which will run "forever", with the task of updating an object.
This is the main :
#include "stdafx.h"
#include <iostream>
#include <windows.h>
#include <cstdlib>
#include <thread>
#include <iostream>//debug only
#include <fstream> //debug only
#include "dataCollectorFTL.h"
int _tmain(int argc, _TCHAR* argv[])
{
dataCollectorFTL dataCollector1;
//Launch thread which will run forever and get the data flows
dataCollector1.runDataCollector();
while(true){
//application running
}
return 0;
}
This is the ".h" of the class
#ifndef DATACOLLECTORFTL_H_INCLUDED
#define DATACOLLECTORFTL_H_INCLUDED
#include <thread>
class dataCollectorFTL {
public:
void runDataCollector();
void getData();
//constructor, destructor
dataCollectorFTL();
~dataCollectorFTL();
private:
HANDLE hProcess;
std::thread dataCollectorThread;
};
#endif // DATACOLLECTORFTL_H_INCLUDED
And finally the ".cpp"
#include "stdafx.h"
#include <iostream>
#include <windows.h>
#include <thread>
#include "dataCollectorFTL.h"
void dataCollectorFTL::runDataCollector(){
//lauch a non-local thread
dataCollectorThread = std::thread(&dataCollectorFTL::getData, this);
}
void dataCollectorFTL::getData(){
//some stuff
}
dataCollectorFTL::dataCollectorFTL(){
//some stuff
}
dataCollectorFTL::~dataCollectorFTL(){
dataCollectorThread.join();
}
The problem is that when I run it, it gaves me this two errors :
Error 1 error C2248: 'std::thread::operator =' : cannot access private member declared in class 'std::thread' c:\users\damien\documents\visual studio 2012\projects\recherche\recherche\datacollectorftl.h 233 1 Recherche
Error 4 error C2248: 'std::thread::thread' : cannot access private member declared in class 'std::thread' c:\users\damien\documents\visual studio 2012\projects\recherche\recherche\datacollectorftl.h 233 1 Recherche
To save time, I can tell you that :
include in the .h doesn't change anything
The content of the runDataCollector methods doesn't change anything. Even if it is empty I still got the problem
std::thread dataCollectorThread can be public or private, it doesn't change anything
If I don't declare as a member of the class, I have a crash of the program because I don't join() the thread in runDataCollector(). And I don't want to join it, has getData() is a while(true) function where it gets data from another soft.
Thank you very much for the time you spent reading this, and thank you again for any help.

Answer 1

I understand that it was some time ago, but I bumped into the problem with same symptoms, and was able to solve it since my compilator (VC110 shipped with VS2012) was a little bit more verbose about what's the problem, so maybe it will help somebody.
I wanted to use this struct:
struct WorkerThreadContext
{
std::thread worker;
... some other attributes ...
}
in a std::vector. Build resulted in error message:
d:\code\testroom\t2\t2\t2.cpp(16): error C2248:
'std::thread::thread' : cannot access private member declared in class 'std::thread'
c:\program files (x86)\microsoft visual studio 11.0\vc\include\thread(73) : see declaration of 'std::thread::thread'
c:\program files (x86)\microsoft visual studio 11.0\vc\include\thread(32) : see declaration of 'std::thread'
This diagnostic occurred in the compiler generated function WorkerThreadContext::WorkerThreadContext(const WorkerThreadContext &)'
Key part is the last sentence - it seems that compiler has a problem to generate implicit copy constructor for my struct, so I changed it to:
struct WorkerThreadContext
{
std::thread worker;
... other attributes ...
WorkerThreadContext() {}
// added explicit copy constructor
WorkerThreadContext(const WorkerThreadContext&) {}
};
and was able to compile the code.
Edit: I almost forget. The reason why the compiler has a problem with this is, that std::thread objects cannot be copied (std::thread::operator=) so the compiler has a problem to construct implicit copy constructor, because it doesn't know how to copy the 'std::thread' object. Which also means, that if you put there explicit copy constructor as the one I wrote, your members (including the 'std::thread' one become invalid). You may (and you should) of course initialize the rest of the struct, however std::thread will remain uninitialized, because you cannot copy it.

Answer 2

When you pass a function in to the std::thread constructor, it needs to be callable from file-scope. In other words, if it's a member function, that function needs to be static. You can still pass in this - just tell the function to expect it.
In other words:
Add the following to the class declaration:
private:
void getData(); // Moved from public!
static void myGetData(DataCollectorFTL *ftl);
Write myGetData:
void DataCollectorFTL::myGetData(DataCollectorFTL *ftl) {
ftl->getData();
} // DataCollectorFLT::myGetData(ftl)
Change the call to std::thread()
//lauch a non-local thread
dataCollectorThread = std::thread(&myGetData, this);