Symbol_table_entry class is a base class. Several different subclasses of symbol table entries will be derived from this class, each designed to store and provide attribute information for the various identifiers that are encountered in the source program.

Symbol table entry base class

Public members:

virtual string get_name() {return name;}
virtual TypeInfo get_type() {return 0;}
virtual int is_variable() {return 0;}
virtual int is_keyword() {return 0;}
virtual int is_proc() {return 0;}
virtual int is_function() {return 0;}
virtual int is_function_result() {return 0;}
virtual int is_parameter() {return 0;}
virtual int is_array() {return 0;}
virtual void print ();

Symbol_table_entry () {;}
Symbol_table_entry (string Name) {name = Name;}
string name;

• The only piece of data common to all symbol table entries is the character string containing the string's identifier.
• TypeInfo is an enumerated type with two values: integer and real.
• Protected members are available only to classes derived from the base class. The actual implementation of the data member name is protected, so a special member function get_name() is publically provided.
• Virtual function members of the base class are provided so that we can invoke the corresponding functions for specific objects. The print function in particular will differ for each type of entry.

You need classes for the following entry types. The required fields are indicated for each.

• Keyword_entry
  • name
• Constant_entry
  • name, type
• Variable_entry
  • name, type, address
• Procedure_entry
  • name, number of parameters, pointer to parameter information
• Function_entry
  • name, type, number of parameters, pointer to parameter information, pointer to result variable (a Variable_entry)
• Array_entry
  • name, type, upper bound, lower bound, address
• Function_result_entry
  • name, type, address

Note that function result variables are just simple variables (i.e., they have the same fields), except that the method is_function_result is defined differently.

Here is one example of an implementation for the derived classes for Variable_entry class. Note that the virtual functions is_variable and print are redefined. Note also that a value is passed to the constructor to set the return value of is_parameter appropriately; since it defaults to 0, this value can be omitted when instantiating a variable entry that is not a parameter. You will have to do the same thing for array entries, which can also be parameters.

Public members:

Variable_entry() {;}
Variable_entry(string Name, TypeInfo Type, int p=0);
/* inside this constructor set parm = p */
int is_variable() {return 1;};
int is_parameter() {return parm;};
void print();

TypeInfo type;
int address;
int parm;