typeid operator in C++ with Examples

typeid is an operator in C++. 

• It is used where the dynamic type or runtime type information of an object is needed.
• It is included in the <typeinfo> library. Hence inorder to use typeid, this library should be included in the program.
• The typeid expression is an lvalue expression.

Syntax:

typeid(type);
OR
typeid(expression);

Parameters: typeid operator accepts a parameter, based on the syntax used in the program:  

• type: This parameter is passed when the runtime type information of a variable or an object is needed. In this, there is no evaluation that needs to be done inside type and simply the type information is to be known.
• expression: This parameter is passed when the runtime type information of an expression is needed. In this, the expression is first evaluated. Then the type information of the final result is then provided.

Return value: This operator provides the runtime type information of the specified parameter and hence that type information is returned, as a reference to an object of class type_info.
Usage: typeid() operator is used in different way according to the operand type. 

1. When operand is a variable or an object.
   
   CPP

   // C++ program to show the use of typeid operator
   
   #include <iostream>
   #include <typeinfo>
   using namespace std;
   
   int main()
   {
       int i, j;
       char c;
   
       // Get the type info using typeid operator
       const type_info& ti1 = typeid(i);
       const type_info& ti2 = typeid(j);
       const type_info& ti3 = typeid(c);
   
       // Check if both types are same
       if (ti1 == ti2)
           cout << "i and j are of"
                << " similar type" << endl;
       else
           cout << "i and j are of"
                << " different type" << endl;
   
       // Check if both types are same
       if (ti2 == ti3)
           cout << "j and c are of"
                << " similar type" << endl;
       else
           cout << "j and c are of"
                << " different type" << endl;
   
       return 0;
   }
   Output

   i and j are of similar type
   j and c are of different type

2. When operand is an expression.
   
   CPP

   // C++ program to show the use of typeid operator
   
   #include <iostream>
   #include <typeinfo>
   using namespace std;
   
   int main()
   {
       int i = 5;
       float j = 1.0;
       char c = 'a';
   
       // Get the type info using typeid operator
       const type_info& ti1 = typeid(i * j);
       const type_info& ti2 = typeid(i * c);
       const type_info& ti3 = typeid(c);
   
       // Print the types
       cout << "ti1 is of type "
            << ti1.name() << endl;
   
       cout << "ti2 is of type "
            << ti2.name() << endl;
   
       cout << "ti3 is of type "
            << ti3.name() << endl;
   
       return 0;
   }
   Output:

   ti1 is of type f
   ti2 is of type i
   ti3 is of type c