[effective C++] bookNode 01, 02，03

1 C++ = C + C with object + Template (generic programming) + STL

2 use const rather than #define(Macro definition) : 
#define is done by preprocessor, when the compiler gives an error on the value defined by , it's very hard to find the macro definition, because it's not in the symbol list.
ex: use const float CONST_FLOAT = 3.14 rather than #define CONST_FLOAT 3.14
Attention :

1. for const pointer , you need const tow times :  const char* const_name = "Auth"; But a better solution is use string: cosnt std::string const_name("Auth");
2. for const member : you need it to be a const, and you need the class has the object, so you need static : class A{private:  static const int Num = 5;}
3. #define macro cannot define a class const member(out of scop)
4.   one solution : enum hack :  enum{Numb = 5}; int scores[Numb]; 
5. Use template inline to replace macro function :
• #define MAX(a,b) f((a)>(b) ? (a) : (b) )// first, you have to add () for every value!(囧)
• then look at this : 
• int a = 5;  b = 0;
• MAX(++a,b);  //a incremented once
• MAX(++a,b+10);  // a incremented twice! the  times that a incremented depends on the other value ! 囧
• So it's better to use   template inline :
• template<typename T> inline  const T& a, const T& b){
•               f(a>b?a:b);
• } 
6. with const, enum, inline, we can less use the macro, but #include, #ifdef, #ifndef are still used. 

3 Use const whenever possible

1. Const pointer, const data, const pointer pointed to const data 
•  const on the left of * : for data; const on the right of *:for pointer
• const ClassA * pa; ClassA const *pa; //----> a pointer pointed to a const object, this object cannot be changed
• ClassA * const pa; //----> a const pointer pointed to an object, the object can be changed
• const ClasssA * const pa //----> a const pointer pointed to a const object
2.  const method returned value ex:
• const Rational operator* (const Rational& a, const Rational& b)//--> why?
• (a*b) = c; //-> because how do you know you client will not do this ? (he want to do assignement(赋值) to the result of an operator!)
3.  const method parameter: simple, it's for avoid when you write == to =.
4.  const method : this method cannot modify the class members :
• class TextBook{
• public:
•         getName() const; //just get, do not change
• }
5.