use of deleted function error

Question

i have had a problem with /usr/include/c++/4.6/ext/new_allocator.h:108:9: error: use of deleted function ‘SMIBQueue::SMIBQueue(const SMIBQueue&)’ with C++ eclipse.

and i am using -std=c++0x flag to use C++11

though i found the point that the error occur at, i don't know why.

this is header file

class SMIBQueue{ private: std::queue<unsigned char> exceptionQueue; std::queue<UserRequest*> userInputQueue; std::queue<LpRsp*> lpRspQueue; std::queue<LpCmd*> lpCmdQueue; std::mutex EvtQueueLock; std::mutex UserQueueLock; std::mutex LpRspQueueLock; std::mutex LpCmdQueueLock; public: int evtGetItem(unsigned char &item); int evtPutItem(unsigned char item); int userGetItem(UserRequest*& item); int userPutItem(UserRequest* item); int lpGetItem(LpCmd*& queue_buf); int lpPutItem(LpCmd *queue_buf); int lpRspGetItem(LpRsp*& queue_buf); int lpRspPutItem(LpRsp *queue_buf); int lpRemoveQueuedInfo(); int lpRspRemoveQueuedInfo(); }; class SMIBQueues{ public: static std::vector<SMIBQueue> smibQueues; static void queueInit(int numOfClient); static int evtGetItem(int sasAddr, unsigned char &item); static int evtPutItem(int sasAddr, unsigned char item); static int userGetItem(int sasAddr, UserRequest*& item); static int userPutItem(int sasAddr, UserRequest* item); static int lpGetItem(int sasAddr, LpCmd*& queue_buf); static int lpPutItem(int sasAddr, LpCmd *queue_buf); static int lpRspGetItem(int sasAddr, LpRsp*& queue_buf); static int lpRspPutItem(int sasAddr, LpRsp *queue_buf); static int lpRemoveQueuedInfo(int sasAddr); static int lpRspRemoveQueuedInfo(int sasAddr); };

and this is the function that the error occur at

std::vector<SMIBQueue> SMIBQueues::smibQueues; void SMIBQueues::queueInit(int numOfClient){ for(int i = 0 ; i < numOfClient; i++){ SMIBQueue s; smibQueues.push_back(s); } }

in this function, push_pack method makes the error. when i eliminate the part, there is no problem while compiling.

Filip Roséen · Accepted Answer · 2014-05-30 10:44:29Z

std::mutex has a deleted copy-constructor, this means that SMIBQueue will have its copy-constructor implicitly deleted since the compiler cannot generate one for you.

How would it go about copying a class which has members that cannot be copied? You will explicitly need to define your own copy-constructor if you want SMIBQueue to be copyable.

WHERE DOES MY CODE REQUIRE A COPY TO BE MADE?

When you are calling smibQueues.push_back (s) a copy of s will be stored inside smibQueues, which requires (the implicitly deleted) copy-constructor.

You can circumvent this specific problem by using smibQueues.emplace_back () to default-construct a SMIBQueue directly inside your smibQueues (ie. std::vector).

^{Note: Just keeo in mind that smibQueues might require SMBIQueue to be copyable/movable during other operations, such as if it tries to resize the underlying buffer, etc.}

RECOMMENDED SOLUTION

Define your own copy-constructor if you plan to use it in contexts which require copying, but do keep in mind that std::mutex is neither copyable or movable, according to the Standard.

Or just call smibQueues.resize(smibQueues.size() + numOfClient) to implicitly construct all the extra entries.
Even with emplace_back() the problem will persist. Vectors still need to be able to copy or move their objects during resizing (moving being preferred in C++11, obviously). Once again, however, std::mutex is required to be neither, and in fact mandated by the standard to be just the opposite. C+11 30.4.1.2 [thread.mutex.requirements.mutex] dictates specifically that "The mutex types shall not be copyable or movable." Punch up the code for the generic emplace_back() with the OP's class def as-presented and it still won't work.
@WhozCraig sure, doing a resize the elements must be movable/copyable, I was directly addressing the problem with the line in question. I'll edit my answer to reflect this.
@FilipRoséen-refp Sure. Btw, smibQueues.emplace_back() (empty parens important) will work with a std::deque<>.

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