Three uses of static keyword

stay C In language ,static Keywords are 3 Common usage methods ：
1.static Modify local variables
2.static Modify global variable
3.static Modify function

1. When static When modifying a local variable , Let's look at the following code ：

int main()
{
    
	for (int i = 0; i < 3; i++)
	{
    
		static int a = 0;
		a++;
		printf("%d ", a);
	}
	return 0;
}

Output is ：

When removing int Ahead static when , The results are as follows ：

When there is no static when , The result is 3 individual 1, It's easy for us to understand ,3 Secondary cycle , Every time you enter the cycle ,a The values are 0, So the output of three cycles is 1; When there is static When decorating , Look at the output , Every time you enter the cycle a The value of is at the end of the last cycle a Value , That is, after entering the cycle ,a The value of is not initialized to 0, let me put it another way , By static The modified local variable is out of scope , The life cycle is not over , Until the end of the whole process , The life cycle will end .

2. When static When modifying global variables , Let's look at the following code ：


First of all we have test_1.c Create a global variable in this source file a, We will in test.c Make a statement , And then print a Value , The result is 10.
When we use static Modify this global variable , Then print a The value of will be wrong ,

He said a For unresolved external symbols , And we are a The source file to which it belongs （ namely test_1.c） To print in a Value , It can be output normally , So when static When modifying global variables , The modified variable scope is the source file where the variable is located .

3. When static When modifying a function , You can verify it by yourself , Let me tell you the conclusion first ,static When modifying a function , The decorated function can only be used in the source file of the function , This function cannot be called in other source files , This is similar to modifying global variables .