Some other functions are also supported with the help of JExel. Expression may contain undefined variables in them, unlike the example given above.Any variable can be used on LHS any number of times.RHS may contain nested expression with both numbers and variables.Numbers or other expressions are not allowed in LHS Each expression can have only a variable on LHS.Note from the example in the previous section that the input file has a specific structure. Finally, the program performs various optimization techniques, such as Constant folding, Algebric simplification, Copy propagation and Dead code removal to give final optimized code. The content of input file is converted to 3-address codes which may contain many redundancies. Insertion and lookup are O(log 2 n) on average.CodeConvert takes input in the form of text file which contains arithmetic expressions.All names are created as child of root node that always follow the property of binary search tree.Another approach to oimplement symbol table is to use binary search tree i.e.Advantage is wuick search is possible and disadvantage is that hashing is complicated to implement.Insertion and lookup can be made very fast – O(1).To search for a name we use hash function that will result in any integer between 0 to tablesize – 1.A hash table is an array with index range: 0 to tablesize – 1.These entries are pointer pointing to names of symbol table.In hashing scheme two tables are maintained – a hash table and symbol table and is the most commonly used method to implement symbol tables.A pointer “First” is maintained to point to first record of symbol table.Searching of names is done in order pointed by link of link field.This implementation is using linked list.Advantage is that it takes minimum amount of space.Insertion is fast O(1), but lookup is slow for large tables – O(n) on average.While inserting a new name we must ensure that it is not already present otherwise error occurs i.e.To search for a name we start from beginning of list till available pointer and if not found we get an error “use of undeclared name”.A pointer “available” is maintained at end of all stored records and new names are added in the order as they arrive.In this method, an array is used to store names and associated information.Operations of Symbol table – The basic operations defined on a symbol table include:įollowing are commonly used data structure for implementing symbol table :. Number and type of arguments passed to function.For parameters, whether parameter passing by value or by reference.If structure or record then, pointer to structure table.Information used by compiler from Symbol table: Symbol Table entries – Each entry in symbol table is associated with attributes that support compiler in different phases. Target Code generation: Generates code by using address information of identifier present in the table.Code Optimization: Uses information present in symbol table for machine dependent optimization.Intermediate Code generation: Refers symbol table for knowing how much and what type of run-time is allocated and table helps in adding temporary variable information.
to verify that expressions and assignments are semantically correct(type checking) and update it accordingly.
It is built in lexical and syntax analysis phases.it stores information about scope and binding information about names, information about instances of various entities such as variable and function names, classes, objects, etc.
Symbol Table is an important data structure created and maintained by the compiler in order to keep track of semantics of variable i.e.