Scope - Static and Dynamic

May 24, 2012Download as pptx, pdf19 likes40,576 views

This document discusses scope in programming languages. Scope refers to the context where a variable name is valid and can be used. There are two types of scope: static and dynamic. With static scope, a variable's scope is the block of code it is defined in such as a function. With dynamic scope, a variable's scope is the period of time a function executes, so the variable remains accessible after the function returns. The key difference is that static scope searches parent blocks for variable names while dynamic scope searches called functions.

PRINCIPLE OF
PROGRAMMING LANGUAGES

SCOPE
STATIC AND DYNAMIC

SNEH PAHILWANI
SYMBIOSIS INSTITUTE OF TECHNOLOGY

In computer programming, a scope is the
context within a computer program in which
a variable name or other identifier is valid and
can be used, or within which
a declaration has effect.

Outside of the scope of a variable name,
the variable's value may still be stored, and
may even be accessible in some way, but the
name does not refer to it; that is, the name is
not bound to the variable's storage.

 Also called lexical scoping.

 If a variable name's scope is a certain
function, then its scope is the program
text of the function definition: within that
text, the variable name exists, and is
bound to its variable, but outside that
text, the variable name does not exist.

Output:
2
3

•Encounter occurrence of
„x‟.
•Search local block
variables
•If not there, keep
searching in parent blocks.
•If not there too, in global
scope then.
•Otherwise „error‟

 In dynamic scoping (or dynamic scope),
if a variable name's scope is a certain
function, then its scope is the time-period
during which the function is executing.

 While the function is running, the variable
name exists, and is bound to its variable,
but after the function returns, the
variable name does not exist.

Pointing the difference out
•Under static scoping: prints out
2
2
•Under dynamic scoping: prints out
3
4
•At “runtime” one searches for
the declaration
•Search in local variables
•If not found, search in local
variables of the caller
•If not found, search in global
variables
•Otherwise error

www.wikipedia.org
http://cseweb.ucsd.edu/cl
asses/sp05/cse130/lecture_
notes/scoping_student.txt

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Scope - Static and Dynamic

1. PRINCIPLE OF PROGRAMMING LANGUAGES SCOPE STATIC AND DYNAMIC SNEH PAHILWANI SYMBIOSIS INSTITUTE OF TECHNOLOGY

2. In computer programming, a scope is the context within a computer program in which a variable name or other identifier is valid and can be used, or within which a declaration has effect. Outside of the scope of a variable name, the variable's value may still be stored, and may even be accessible in some way, but the name does not refer to it; that is, the name is not bound to the variable's storage.

3. SCOPE STATIC DYNAMIC

4.  Also called lexical scoping.  If a variable name's scope is a certain function, then its scope is the program text of the function definition: within that text, the variable name exists, and is bound to its variable, but outside that text, the variable name does not exist.

5. Output: 2 3 •Encounter occurrence of „x‟. •Search local block variables •If not there, keep searching in parent blocks. •If not there too, in global scope then. •Otherwise „error‟

6. SCOPE STATIC DYNAMIC

7.  In dynamic scoping (or dynamic scope), if a variable name's scope is a certain function, then its scope is the time-period during which the function is executing.  While the function is running, the variable name exists, and is bound to its variable, but after the function returns, the variable name does not exist.

8. Pointing the difference out •Under static scoping: prints out 2 2 •Under dynamic scoping: prints out 3 4 •At “runtime” one searches for the declaration •Search in local variables •If not found, search in local variables of the caller •If not found, search in global variables •Otherwise error

9. www.wikipedia.org http://cseweb.ucsd.edu/cl asses/sp05/cse130/lecture_ notes/scoping_student.txt

Scope - Static and Dynamic

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