"C Language" local variables, global variables, local static variables, global static variables, extern,static differences

Local variables:

Created on the stack (growing down), the life cycle exists in the current scope.

is a random value if it is not initialized at the time of creation.

Global variables:

Created in the static zone, the life cycle is always present.

0 if it is not initialized at the time of creation.

Static local variables:

The external link properties are severed. Created in the static zone.

0 if it is not initialized at the time of creation.

The storage of global variables and static variables is placed in a block, initialized global variables and static variables in an area, uninitialized global variables and uninitialized static variables in another adjacent area.

Global static variables:

The external link attribute is cut off and created in the static zone, and the life cycle persists.

0 if it is not initialized at the time of creation.

#include <stdio.h> #include <stdlib.h>int fun1 () {static int n = 0;    n++; return n;}    int main () {int ret = 0;        for (int i = 0; i < ten; i++) {ret = FUN1 ();    printf ("%d\n", ret);    } system ("Pause"); return 0;}

Output-------... 10.

#include <stdio.h> #include <stdlib.h>static int n;int fun1 () {n = 0;    n++; return n;}    int main () {int ret = 0;        for (int i = 0; i < ten; i++) {ret = FUN1 ();    printf ("%d\n", ret);    } system ("Pause"); return 0;}

Output 10 x 1.

extern

External file can be detected with external link properties.

Static

Cut off external link properties.

Variables located in the static zone:

The entire life cycle exists, such as global variables, static variables.

#include <stdio.h> #include <stdlib.h>int b = 20;int Main () {static int a = 10;    int c = 5;    printf ("%p\n", &a);    printf ("%p\n", &b);    printf ("%p\n", &c);    System ("pause"); return 0;}

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It can be concluded that the storage address of the static variable and the global variable is very close, in the same region, namely: are stored in the static zone.

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C language Local variables, global variables, local static variables, global static variables, extern,static differences