What actually compiler does when we declare static variables?

Question

I want to know what actually going under the hood,how compiler treats static variables. Unlike auto variable, static variable\'s value persist even after the end of block bu

Answer 1

static variables are global variables with limited scope. @user3386109

1. static/global variables exist for the lifetime of the program.

2. static/global are initialized at program start-up to either:

   A. If not explicitly initialize: to the bit pattern 0.
   B. Otherwise to to an explicit value like double x = 1.23;

3. static variables scope is either limited to

   A. If defined outside a function: file scope, only code within the file can "see" the variable.
   B. If defined inside a function: block scope: only code within the block may "see" the variable.

4. There is only one instance of the static variable within its scope unless a lower scope defines another with the same name. The compiler "knows" which same named variable to access by using the closest scope first. It is not re-created or re-initialized, even if inside a function.

Note: With multiple threads, other considerations apply - not shown.

static int fred = 11;
int sally = 21;

void foo2(void) {
  static int fred = 31;
  int sally = 41;
  printf("static %d non-static %d\n", fred++, sally++);
  {
    printf("static %d non-static %d\n", fred++, sally++);
    {
      static int fred = 51;
      int sally = 61;
      printf("static %d non-static %d\n", fred++, sally++);
    }
  }
}

int main(void) {
  printf("static %d non-static %d\n", fred++, sally++);
  foo2();
  printf("static %d non-static %d\n", fred++, sally++);
  foo2();
  return 0;
}

Output

static 11 non-static 21
static 31 non-static 41
static 32 non-static 42
static 51 non-static 61
static 12 non-static 22
static 33 non-static 41
static 34 non-static 42
static 52 non-static 61