Understanding-and-Using-C-pointers

#### 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。