c++ - Cast a void pointer to a struct or memcpy to new struct?

I am passing a void * as an argument to a function foo(void* parm) which calls function bar(STmyStruct* parm)
Should I cast the void pointer to STmyStruct* or create a new struct, memcpy what the void* points to and then pass a pointer to that struct?
I guess solution A is more efficient?

A:    foo(void* parm)
      {
       bar((STmyStruct*) parm)
      }

B:    foo(void* parm)

      {
       STmyStruct myStr;
       memcpy(&myStr, parm, sizeof(STmyStruct));
       bar(&myStr)
      }


bar(STmyStruct* mystr);