The use of C language static can flexibly change the life cycle and make you write code like a duck to water

stay C In language static Is a very important keyword

static Means static , Its usage is basically divided into three kinds

1. Modify local variables （ Change the life cycle of local variables ）

2. Modify global variable （ Make the global variable only act on the current source file ）

3. Modify function （ Make the function only work with the current source file ）

How to decorate it ？ and Life cycle And how it was changed ？

Let me give you an example , Let's take a look at

First write a string to take a The code of the address

Now let's run this code , take a Take a look at the address of

a The address for 00eff748

good , Let's run it again

  Will find ,a The address of has become 012ff8b4

a The address of has changed ,a Of Life cycle There is only one cycle

Because a In fact, there is a keyword hidden in front of auto

auto Means automatic , It is an automatic variable , Automatically create , Automatically destroy

If we don't hide our code, it's like this

auto It's generated automatically , Even if you delete it , It's still there

Then how can we change a The life cycle of , Now static That comes in handy

As long as we are int a = 0; prefix static That's all right. , use static hold auto Replace

  At this time, we will find that , No matter how many times ,a The address of has changed into one Set value

  We can draw a conclusion ,static hold a Of Life cycle Changed the

Of course ,static Not just for addresses , It's in loop The performance is also excellent

You can see , The above two groups of codes , One with static modification , None

There is no code on the left static modification a, therefore a Of Life cycle There is only one cycle , At the end of a cycle, it will be reset to 1

therefore printf The printed result is 2 2 2 2 2 2 2 2 2 2

And the code on the right has a static modification ,a Of Life cycle Be extended , The feature of automatic destruction is cancelled , So in each cycle a The value of +1

therefore printf The printed result is 2 3 4 5 6 7 8  9 10 11 

Yes , One more thing to add  

static Modify local variables , On the surface, it changes the life cycle of local variables

In essence, it changes the storage type of variables , From stack area to static area

（ Memory is basically divided into several areas , The stack area , Heap area , Static zone ）

  I won't go into details here

stiatic Modify global variable , Change the global variable from acting on the whole project to acting only on the current source file

In essence, it changes the external link attribute of a global variable into an internal link attribute

static Decorate functions with static The essence of modifying global variables is basically the same

Blog for the first time , I have just learned programming 4 God , Please point out any mistakes

Gentlemen, what can you teach me ？