[embedded] - Introduction to four memory areas

One 、 Origin of four memory areas

Program execution runs in memory , And different objects in the program （ Such as The pointer , local variable , Global variables , Function parameter wait ） The required life cycle is different , So put these objects in different sections , This gives these objects different lifecycles , Four memory areas come from this .

Two 、 Introduction to four memory areas

Memory four is divided into ： The stack area , Heap area , Global area , Code section .

1. The stack area （stack）

Stack area is automatically allocated and released by compiler .

The stack area mainly stores function parameters 、 Function return value 、 local variable .

2. Heap area （heap）

Heap area is manually allocated and released by programmer . If the programmer does not release , At the end of the program , Released by the system .

The stacking area is mainly stored by malloc Keyword applied memory space . stay C++ Keywords in language new The requested memory is also in the heap .

3. Global area

The global area is also called data area or static area .

The overall situation is divided into three segments ： data paragraph 、bss paragraph 、rodata paragraph .
（1）.data Segment storage has been initialized and the value is not 0 And static variables
（2）.bss The segment storage is uninitialized and the initialization value is 0 And static variables .
（3）.rodata Segments store various constants , Such as ：const、 character string 、#define etc.

data  Duan also called  RW-data  paragraph 
bss  Duan also called  ZI-data  paragraph 
rodata  Segments are also called constant areas or read-only storage areas 

4. Code section （text）

Code area is also called code paragraph or text paragraph .

Used to store program code , Managed by the operating system , read-only .

3、 ... and 、 Add extra

flash perhaps ROM The data is still saved after power failure , The saved data are RO-data、RW-data、 Code section

RAM Generally speaking, it means sdram, Fast running speed , But the power down data will be lost , The saved data are The stack area 、 Heap area 、 Data area

Be careful ：
1,flash perhaps ROM Why not save ZI-data？
ZI-data Segment data is not initialized or initialized to 0, When starting the system, directly put this flash perhaps ROM clear 0 that will do , No need to save .
2,RW-data yes RAM The use of , Why store to flash or ROM in ？
RW-data This part of the variable has been initialized , There is only RAM Power loss will result in loss , So you need to be in flash or ROM Store a copy of