Using static mutex in a class

I have a class that I can have many instances of. Inside it creates and initializes some members from a 3rd party library (that use some global variables) and is not thread-safe.

I thought about using static boost::mutex, that would be locked in my class constructor and destructor. Thus creating and destroying instances among my threads would be safe for the 3rd party members.

class MyClass

  static boost::mutex mx;

  // 3rd party library members

  boost::mutex::scoped_lock scoped_lock(mx);
  // create and init 3rd party library stuff

  boost::mutex::scoped_lock scoped_lock(mx);
  // destroy 3rd party library stuff

I cannot link because I receive error:

undefined reference to `MyClass::mx`
  1. Do I need some special initialization of such static member?

  2. Is there anything wrong about using static mutex?

Edit: Linking problem is fixed with correct definition in cpp

boost::mutex MyClass::mx;


You have declared, but not defined your class static mutex. Just add the line

boost::mutex MyClass::mx;

to the cpp file with the implementation of MyClass.

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