從Google C++ Coding Style裡面抽出一些貼近現實的rule

ref a class have two methods, one is #include, one is forward declaration, and the later can reduce dependence recompilation when referenced header file changes.

Define functions inline only when they are small, say, 10 lines or less. Typically, the accessor and mutator

place a function's variable in the narrowest scope possible, and initialize variables in the declaration. e.g.
while (const char* p = strchr(str, '/')) str = p + 1;

static class member variables, and function static variables, must be Plain Old Data (POD): only ints, chars, floats, or pointers, or arrays/structs of POD.
If you need a static or global variable of a class type, consider initializing a pointer (which will never be freed), from either your main() function or from pthread_once(). Note that this must be a raw pointer, not a "smart" pointer.

In general, constructor should merely set member variables to their inital values, any complex initialization should go in an explicit Init(). and Don't throw exception in constructor, carefully access potentially uninitialized global variables

Disable copy and assignment operator if that is not necessary

// This should be used in the private: declarations for a class
#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
  TypeName(const TypeName&);               \
  void operator=(const TypeName&