Organization for Block
Structured Languages:
- The block structured language is a kind of language in which sections of source code is within some matching pair of delimiters such as “{“ and “}” or begin and end
- Such a section gets executed as one unit or one procedure or a function or it may be controlled by some conditional statements (if, while, do-while)
- Normally, block structured languages support structured programming approach
Example:
C, C++, JAVA, PASCAL, FORTRAM, LISP and SNOBOL
- Non-block structured languages are LISP, FORTRAN and SNOBOL
Implementation of
Symbol Table:
- Each entry in the symbol table can be implemented as a record with several fields
- The following data structures are used for organization of block structured languages:
Linear
List
Self-Organizing
List
Hashing
Tree Structure
Symbol table
organization using Linear List:
- A linear list of records is the easiest way to implement the symbol table
- In this method, an array is used to store names and associated information
- The new names are added to the symbol table in the order they arrive
- The pointer “available” is maintained at the end of all stored records
- To retrieve the information about some name we start from beginning of array and go on searching up to available pointer. If we reach at pointer available without finding a name we get an error “use of undeclared name”
- While inserting a new name we should ensure that it is not already present. If it is already present then another error occurs, i.e., “Multiple Defined Name”.
Advantages:
- It takes minimum amount of space
- Additions are simple
- Limitations
- Higher access time
Linear List as
follows:
Name 1
|
Information 1
|
Name 2
|
Information 2
|
.
|
.
|
.
|
.
|
.
|
.
|
.
|
.
|
Name n
|
Information n
|
Symbol Table
organization using self-Organizing List:
- In this method, symbol table is implemented using linked list. A link field is added to each record
- We search the records in the order pointed by the link of link field
- A pointer “First” is maintained to point to first record of the symbol table
- The reference to these names can be Name 3, Name 4, Name 2
- When the name is reference or created, it is moved to the front of the list
- The most frequently referred names will tend to be at the front of the list. Hence, access time to most frequently referred names wil be the least
Advantages
- It takes minimum amount of space
- Additions are simple
- Limitation
- Higher access time
