1. Item1: View C++ as a federation of languages

C++ is not a unified language with a single set of rules; its a federation of four sublanguages， each with its own conventions. The four sublanguages are: 

　　（1） C.   

　　（2） Object-Oriented C++: This part of C++ is what C with Classes was all about: classes， encapsulation， inheritance， polymorphism， virtual functions， etc. 

　　（3）Template C++: This is the generic programming part of C++. Template is used a lot in C++.

　　（4）The STL: The STL is a template library with its own conventions. When you are working with the STL， you need to be sure to follow its own conventions.

Keep these four sublanguages in mind， and dont be surprised when you encounter situations where effective programming requires that you change strategy when you switch one sublanguage to another.

2. Item2: Prefer const， enum， and inline to ＃define

Using ＃define has many drawbacks. Therefore， we should use const， enum and inline instead of ＃define.

• For simple constants， prefer const objects or enums to ＃define.


• For function-like macros， prefer inline functions to ＃define.

3. Item3: Use const whenever possible

If the word const appears to the left of the asterisk， whats pointed to is constant; if the word const appears to the right of the asterisk， the pointer itself is constant; if const appears on both sides， both are constant.

const char  p = greetings;   //const data， non-const pointer

char  const p = greetings;   //const pointer， non-const data

const char  const p = greetings;   //const pointer， const data

char const  p = greetings;  //const pointer， non-const data（compare with the second one）

const Member Functions:

The purpose of const on member functions is to identify which member functions may be invoked on const objects. Non-const functions can only be invoked on non-const objects， while const functions can be invoked on both const and non-const functions. 

Declaring something const helps compilers detect usage errors. Const can be applied to objects at any scope， to function parameters and return types， and to member functions as a whole.

4. Item4: Make sure that objects are initialized before theyre used

• Manually initialize objects of built-in type， because C++ only sometimes initializes theme itself.


• In a constructor， prefer use of the member initialization list to assignment inside the body of the constructor. List data members in the initialization list in the same order theyre declared in the class.