Lecture 3 | NotionNext BLOG

stack

local vars

heap

dynamically allocated vars

code/data

global vars
static global vars
static local vars

Global vars

vars defined outside any functions

can be shared btw .cpp files

extern

extern

extern is a declaration says there will be such a variable somewhere in the whole program

“such a” means the type/name of the variable

global variable is a definition, the storage place for that variable

定义的地方是真正创建 vars 的地方，会在这里分配空间给 vars

static

static global variable inhibits the access outside its .cpp file, so as the static function

static local vars

keep its state in between multiple visits to its function, and is initialized at its first access

两大特性：

restricted access scope

persistent storage

Pointers to objects

operators:

get address

ps = &s;

get the object

(*ps).length()

call the function

ps->length()

两种方式：

string s;

创建后自动初始化

string *ps;

指针指向哪还不知道

Reference

char& r = c

相当于 r 是 c 的一个别名，实际是一个东西；任意一方有改动另一方也会一起改动

两种定义形式

type& refname = name;

for ordinary definition
an initial value is required

type& name;

in parameter lists or member variables
initialized by caller or constructor

Rules of references

不可以被重绑定

e.g.

the target of a non-const reference must be an lvalue

no references to references

no pointer to reference, but reference to pointer is ok

no arrays of reference

Dynamic memory allocation

new

delete

new 类似malloc ，delete 类似free

主要的不同在于：

new 会自动调用构造函数，delete 会自动调用析构函数。malloc 和free 只分配释放内存。（没太搞懂析构函数）

Constant

const : declares a variable to have a constant value

默认是 internal linkage，即只能在该 .cpp 内访问

C++ 编译器通常会 在符号表（Symbol Table）中存储常量值，而不是实际分配内存

如果想要跨文件共享 const 常量，需要显式使用 extern 强制分配存储空间

e.g.