Static and dynamic scoping
- 2. What is Scoping ? 1. Scoping refers to the visibility of variables . In simple words , we can say a textual region of program in which binding is active is its scope. 2. A scope is the body of module class , subroutine or structured control flow statement sometimes called as block .
- 3. Types of Scopes: There are 2 types of scopes : 1.Static Scoping 2. Dynamic Scoping • Static Scoping : it is also called as lexical scoping. It is binding between names and object can be determined at compile time. In static scoping the compiler checks for say variable “x” if it is present in local block if it is not there then it search in the main or parent block. • Dynamic Scoping : It is binding between names and object can be determined at run time. In dynamic scoping the compiler checks for say variable “x” if it is present in local block if it is not there then it search in the sibling functions block or from where it is called.
- 4. Example : 1 i n t x ; i n t m a i n ( ) { x = 2 ; f ( ) ; g ( ) ; } V o i d f ( ) { i n t x = 3 ; h ( ) ; } v o i d g ( ) { i n t x = 4 ; h ( ) v o i d h ( ) { p r i n t f ( “ % d ” , x ) ; } Output : • By static rule : x=2 main’s x x=2 main’s x • By dynamic rule : x=3 f()’s x x=4 g()’s x
- 5. Example : 2 B e g i n i n t e g e r m , n ; P r o c e d u r e h a r d y : b e g i n p r i n t ( “ i n h a r d y n = “ , n ) ; e n d ; P r o c e d u r e l a u r e l ( n : i n t ) : b e g i n p r i n t ( “ i n l a u r e l m = “ , m ) ; p r i n t ( “ i n l a u r e l n = “ , n ) ; h a r d y ; e n d ; / / m = 5 0 ; n = 1 0 0 ; p r i n t ( i n m a i n p r o g n = “ , n ) ; l a u r e l ( 1 ) ; h a r d y ; e n d ; Out put : • By st atic r ule : n=100 main’s n m=50 main’s m n=1 l aurel’s n n=100 main’s n n=100 main’s n • By dynamic r ule ( sibling) n=100 main’s n m=50 main’s m n=1 l aurel’s n n=1 ( hardy)laurel ’s n n=100 main’s n
- 6. Example : 3 i n t b = 5 ; i n t f o o ( ) { i n t a = b + 5 ; r e t u r n a ; } i n t b a r ( ) { i n t b = 2 ; r e t u r n f o o ( ) ; } i n t m a i n ( ) { f o o ( ) ; b a r ( ) ; r e t u r n 0 ; } Output : • By static rule : foo=10 (foo‘s return a) bar =10 (foo’s return a) • By dynamic rule : foo=10 (foo‘s return a) bar =7 (bar‘s return foo)