CODEWITHSUNDEEP
c++castingpthreadsvoid-pointers
Galileo
Galileo

Reputation: 321

void* pointer casting while scheduling a thread

I have a function called by a thread.this function has a unique argument which is queue::my_queue . So I need to perform a cast on void pointer in the method called by the thread as follows: 

void *AddPacket(void *Ptr) 
{     queue<int> my_queue = (queue*)Ptr ; 
       my_queue.push(byte) ; 
}

and in the main, I do: 

int main()
{   // do business
  pthread_create(&thread, NULL, &AddPacket, (void*)queue) ; 
}

But both conversions are wrong.

the first conversion leads to the error:

request for member ‘push' in ‘my_queue’, which is of non-class type ‘queue*’

and the second one:

invalid cast from type ‘queue’ to type ‘void*’

How can I solve the problem?

Upvotes: 2

Views: 2148

Answers (3)

Roman Saveljev
Roman Saveljev

Reputation: 2594

You try to cast object type to pointer type. It is not allowed. I guess you are new to C++, so I post corrected code here to unpuzzle you and get you going, but please read a book on C++:

queue<int>* my_queue = (queue<int>*)Ptr ; 
my_queue->push(byte) ;

pthread_create(&thread, NULL, &AddPacket, &queue) ;

Remember to read about pointers on C++ :)

Upvotes: 4

Kerrek SB
Kerrek SB

Reputation: 477562

You need to change both the thread function and the thread creation:

// thread entry point:
void *AddPacket(void *Ptr)
{
    reinterpret_cast<std::queue<int>*>(Ptr)->push(byte);
}


// thread creation:

std::queue<int> q;
pthread_create(&thread, NULL, &AddPacket, &q);
//                                        ^^^^ **pointer** to "q";
//                                        conversion to void* is implied

Upvotes: 1

Martin James
Martin James

Reputation: 24907

Try:

queue<int> *my_queue = (queue<int> *)Ptr ;
my_queue->push(byte) ;

pthread_create(&thread, NULL, &AddPacket, (void*)&queue) ;

.. something along those lines, anyway

Upvotes: 3

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