std::atomic::store can't be called in ctor initialization list

Question

When I was trying to call std::atomic::store in initialization list, I got following compiler error: g++ -std=c++11 test_function_call_in_ctor.cc

test_function_call_in_ctor.cc: In constructor 'TestA::TestA()': test_function_call_in_ctor.cc:7:17: error: expected '(' before '.' token TestA() : run_.store(true) { ^ test_function_call_in_ctor.cc:7:17: error: expected '{' before '.' token

source code as below:

class TestA {
  public:
    TestA() : run_.store(true) {
      cout << "TestA()";
      if (run_.load()) {
        cout << "Run == TRUE" << endl;
      }
    }
    ~TestA() {}
  private:
    std::atomic<bool> run_;
};
int main() {
  TestA a;
  return 0;
}

Any idea on this issue? Thanks a lot.

Answer 1

The initializer list specifies the constructor arguments of the members. You cannot use a member function as you tried. However, std::atomic<T> has a constructor taking a T value as arguemnt:

TestA(): run_(true) { ... }

Since the object is under construction it can't possibly be used by another thread at that time, ie, there is no need to use store() anyway.

Answer 2

Because run_ hasn't been constructed. You should call its constructor in the initializer list:

TestA() : run_(true) {}