C Language Learning-global variables, static local variables

Global variables

• Global variables

Variables defined outside the function are global variables

Global variables have global lifetimes and scopes

They are independent of any function

They can be used inside any function

#include <stdio.h>intFvoid);intGAll = A;intMain () {printf ("GAll in%s function is%d\n", __func__,gall);//Note: The __func__ is the output is which function, the underscore is two consecutive togetherf (); printf ("GAll again in%s function is%d\n", __func__,gall); return 0;}intf () {printf ("GAll in%s function is%d\n", __func__,gall); GAll+=2; printf ("GAll again in%s function is%d\n", __func__,gall); returnGAll;}

• Initialization of global variables

A global variable that does not initialize will get a value of 0

The pointer will get a null value

Global variables can only be initialized with values that are known at compile time

Their initialization occurs before the main function

• Global variables that are hidden

If there is a variable with the same name as the global variable inside the function, the global variable is hidden.

Static local Variables

Adding the static modifier to a local variable definition becomes a static local variable

When the function leaves, the static variable will continue to exist and maintain its value .

The initialization of a static local variable is only done when the function is first entered , and then the value of the function remains last left.

Static local variables are actually special global variables

They are in the same memory area

A static local variable has a global lifetime, and a local scope within the function.

Static here means the local scope (local access)

Functions that return pointers

Returning the address of a local variable is dangerous

Returns the address of a global variable or static local variable is safe

Returns the memory of malloc within the function is secure, but is prone to problems

The best practice is to return the incoming pointer

Tips

Do not use global variables to pass parameters and results between functions

Try to avoid using global variables

Functions that use global variables and static local variables are thread insecure

The End

Thank you!

C Language Learning-global variables, static local variables