Static

• static has several meanings in c++
  • static local variables.
  • static class methods are discussed on 306.
  • static class data members are discussed on 314.
  • There are others, but these three will do.
• static local variables
  • These are declared within a code block. (usually a function)
  • They are declared with the storage class specifier static
  • They are always followed with an initialization statement.
  • static int foo=7
• The semantics are
  • On first entry, the variable is constructed and initialized.
  • On additional entries, the initialization is skipped.
  • The lifetime is extended to the lifetime of the program.
  • But scope is still within the code block.
• They are not the best thing, as they are essentially a work around for global variables.
  • You do know where they were changed, but when becomes a problem.
  • Apparently they cause big problems for testing.
• See staticLocal.cpp.
• Static class methods
  • A static class method is shared by all instances of a class.
  • They are not associated with any instance of a class however.
    • Therefore they do not have access to this
    • And do not have direct access to non-static member data.
  • If public, they can be accessed without any instances of the class being created.
    • You must use class scope to access them ClassT::StaticMember()
  • Don't give me that look they are valuable later.
  • Examples coming, but I need static member variables next.
• Static Member variables.
  • Like static member functions, static member variables are shared across a class.
  • They are not associated with any instance of a class, but with every instance.
  • Due to this, initialization is the only strange part.
  • This can be done in one of two ways

    • class CountedT{
          private:
              // old style
              static size_t count;
              // since c++17
              static inline size_t newCount{0};
      };
      // probably in implementation file, not header file
      // again old style
      size_t CountedT::count{0};
      

  • Access is as normal, but static member functions have access as well.
• See CounterT.h
• See CounterT.cpp
• See CounterMain.cpp
• I also fixed my Makefile. (Mable was right, boy do I hate to admit that)