How to initialize a static std::atomic data member
atomic, c++, c++11, constants, stdatomic
Solution
I know that the atomic types do not have copy constructors, and I assume that explains why this code does not work.
Yes, the error says that quite clearly.
Does anybody know a way to actually get this code to work?
Instead of copy-initialising from a temporary, which requires an accessible copy constructor:
std::atomic<int> order::c = std::atomic<int>(0);
use direct-initialisation, which doesn't:
std::atomic<int> order::c(0); // or {0} for a more C++11 experience
You should probably prefer that anyway, unless you enjoy reading unnecessarily verbose code.
Problem
I would like to generate identifiers for a class named `order` in a thread-safe manner. The code below does not compile. I know that the atomic types do not have copy constructors, and I assume that explains why this code does not work. Does anybody know a way to actually get this code to work? Is there an alternative approach? ``` #include <atomic> #include <iostream> class order { public: order() { id = c.fetch_add(1); } int id; private: static std::atomic<int> c; }; std::atomic<int> order::c = std::atomic<int>(0); int main() { order *o1 = new order(); order *o2 = new order(); std::cout << o1->id << std::endl; // Expect 0 std::cout << o2->id << std::endl; // Expect 1 } ``` Compiling the above results in the following error: ``` order.cpp:45:51: error: use of deleted function ‘std::atomic<int>::atomic(const std::atomic<int>&)’ In file included from order.cpp:3:0: /usr/include/c++/4.7/atomic:594:7: error: declared here ```