#### Why You Should Become Proficient with Pointers
指针的几个用处：
* Creating fast and efficient code
* Providing a convenient means for addressing many types of problems
* Supporting dynamic memory allocation
* Making expressions compact and succinct
* Providing the ability to pass data structures by pointer without incurring a large overhead
* Protecting data passed as a parameter to a function
指针可能出现的几个问题：
* 访问数组和其他数据结构越界
* 引用已经不错在的自动变量
* 在对内容被释放后引用堆内存
* 在指针被分配内存前解引用
pointer的语法和语义都由C specification定义，但有些情况没有显示定义，这种情况下，行为被定义为：
* Implementation-defined
* Unspecified
* Undefined
#### Declaring Pointers
#### How to Read a Declaration
**The trick is to read them backward.**
#### Address of Operator
good practice: initialize a pointer as soon as possible
#### The Concept of Null
几个Null:
* The null concept
* The null pointer constant
* The NULL macro
* The ASCII NUL
* A null string
* The null statement
当NULL被赋值给指针时，意味着这个指针不指向任何东西。
null pointer与未初始化pointer不一样：后者可能包含任何值，前者不指向任何内存位置。
#### To NULL or not to NULL
zero的意义随着上下文而改变。