C++ Program to implement Symbol Table



Prerequisite: Symbol Table

A Symbol table is a data structure used by the compiler, where each identifier in program’s source code is stored along with information associated with it relating to its declaration. It stores identifier as well as it’s associated attributes like scope, type, line-number of occurrence, etc.

Symbol table can be implemented using various data structures like:



  • LinkedList
  • Hash Table
  • Tree

A common data structure used to implement a symbol table is HashTable.

Operations of Symbol table – The basic operations defined on a symbol table include:

Consider the following C++ function:

// Define a global function
int add(int a, int b)
{
int sum = 0;
sum = a + b;
return sum;
}



Symbol Table for above code:

Name Type Scope
add function global
a int function parameter
b int function parameter
sum int local

Below is the C++ implementation of Symbol Table using the concept of Hashing with separate chaining:

// C++ program to implement Symbol Table
#include <iostream>
using namespace std;
  
const int MAX = 100;
  
class Node {
  
    string identifier, scope, type;
    int lineNo;
    Node* next;
  
public:
    Node()
    {
        next = NULL;
    }
  
    Node(string key, string value, string type, int lineNo)
    {
        this->identifier = key;
        this->scope = value;
        this->type = type;
        this->lineNo = lineNo;
        next = NULL;
    }
  
    void print()
    {
        cout << "Identifier's Name:" << identifier
             << "\nType:" << type
             << "\nScope: " << scope
             << "\nLine Number: " << lineNo << endl;
    }
    friend class SymbolTable;
};
  
class SymbolTable {
    Node* head[MAX];
  
public:
    SymbolTable()
    {
        for (int i = 0; i < MAX; i++)
            head[i] = NULL;
    }
  
    int hashf(string id); // hash function
    bool insert(string id, string scope,
                string Type, int lineno);
  
    string find(string id);
  
    bool deleteRecord(string id);
  
    bool modify(string id, string scope,
                string Type, int lineno);
};
  
// Function to modify an identifier
bool SymbolTable::modify(string id, string s,
                         string t, int l)
{
    int index = hashf(id);
    Node* start = head[index];
  
    if (start == NULL)
        return "-1";
  
    while (start != NULL) {
        if (start->identifier == id) {
            start->scope = s;
            start->type = t;
            start->lineNo = l;
            return true;
        }
        start = start->next;
    }
  
    return false; // id not found
}
  
// Function to delete an identifier
bool SymbolTable::deleteRecord(string id)
{
    int index = hashf(id);
    Node* tmp = head[index];
    Node* par = head[index];
  
    // no identifier is present at that index
    if (tmp == NULL) {
        return false;
    }
    // only one identifier is present
    if (tmp->identifier == id && tmp->next == NULL) {
        tmp->next = NULL;
        delete tmp;
        return true;
    }
  
    while (tmp->identifier != id && tmp->next != NULL) {
        par = tmp;
        tmp = tmp->next;
    }
    if (tmp->identifier == id && tmp->next != NULL) {
        par->next = tmp->next;
        tmp->next = NULL;
        delete tmp;
        return true;
    }
  
    // delete at the end
    else {
        par->next = NULL;
        tmp->next = NULL;
        delete tmp;
        return true;
    }
    return false;
}
  
// Function to find an identifier
string SymbolTable::find(string id)
{
    int index = hashf(id);
    Node* start = head[index];
  
    if (start == NULL)
        return "-1";
  
    while (start != NULL) {
  
        if (start->identifier == id) {
            start->print();
            return start->scope;
        }
  
        start = start->next;
    }
  
    return "-1"; // not found
}
  
// Function to insert an identifier
bool SymbolTable::insert(string id, string scope,
                         string Type, int lineno)
{
    int index = hashf(id);
    Node* p = new Node(id, scope, Type, lineno);
  
    if (head[index] == NULL) {
        head[index] = p;
        cout << "\n"
             << id << " inserted";
  
        return true;
    }
  
    else {
        Node* start = head[index];
        while (start->next != NULL)
            start = start->next;
  
        start->next = p;
        cout << "\n"
             << id << " inserted";
  
        return true;
    }
  
    return false;
}
  
int SymbolTable::hashf(string id)
{
    int asciiSum = 0;
  
    for (int i = 0; i < id.length(); i++) {
        asciiSum = asciiSum + id[i];
    }
  
    return (asciiSum % 100);
}
  
// Driver code
int main()
{
    SymbolTable st;
    string check;
    cout << "**** SYMBOL_TABLE ****\n";
  
    // insert 'if'
    if (st.insert("if", "local", "keyword", 4))
        cout << " -successfully";
    else
        cout << "\nFailed to insert.\n";
  
    // insert 'number'
    if (st.insert("number", "global", "variable", 2))
        cout << " -successfully\n\n";
    else
        cout << "\nFailed to insert\n";
  
    // find 'if'
    check = st.find("if");
    if (check != "-1")
        cout << "Identifier Is present\n";
    else
        cout << "\nIdentifier Not Present\n";
  
    // delete 'if'
    if (st.deleteRecord("if"))
        cout << "if Identifier is deleted\n";
    else
        cout << "\nFailed to delete\n";
  
    // modify 'number'
    if (st.modify("number", "global", "variable", 3))
        cout << "\nNumber Identifier updated\n";
  
    // find and print 'number'
    check = st.find("number");
    if (check != "-1")
        cout << "Identifier Is present\n";
    else
        cout << "\nIdentifier Not Present";
  
    return 0;
}

Output:

**** SYMBOL_TABLE ****

if inserted -successfully
number inserted -successfully

Identifier's Name:if
Type:keyword
Scope: local
Line Number: 4
Identifier Is present

if Identifier is deleted

number Identifier updated

Identifier's Name:number
Type:variable
Scope: global
Line Number: 3
Identifier Is present


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