is_lock_free未在std :: atomic中定义 <T> 在gcc 4.7.2？

Question

I encounter this compiler error

function std::atomic::is_lock_free() const: error: undefined reference 
to '__atomic_is_lock_free'

when compiling code like below using gcc 4.7.2 on linux.

struct S {
  int a;
  int b;
};


  std::atomic<S> s;
  cout << s.is_lock_free() << endl;

Answer 1

Atomic API isn't complete in GCC 4.7:

• When lock free instructions are not available (either through hardware or OS support) atomic operations are left as function calls to be resolved by a library. Due to time constraints and an API which is not finalized, there is no libatomic supplied with GCC 4.7. This is easily determined by encountering unsatisfied external symbols beginning with __atomic_* .

Since there is no libatomic shipped with GCC 4.7 you need to use another compiler which actually supports the features you want or provide the missing features ( sample implementation ).