Interface segregation design principle recommends modeling many small interfaces for a specific purpose, as opposed to modeling one bigger interface that represents many things. In the case of C++, an abstract class with pure virtual functions can be thought of as an interface.

Let's take a simple example to understand interface segregation:

#include <iostream>
#include <string>
using namespace std;

class IEmployee {
      public:
          virtual string getDoor() = 0;
          virtual string getStreet() = 0;
          virtual string getCity() = 0;
          virtual string getPinCode() = 0;
          virtual string getState() = 0;
          virtual string getCountry() = 0;
          virtual string getName() = 0;
          virtual string getTitle() = 0;
          virtual string getCountryDialCode() = 0;
          virtual string getContactNumber() = 0;
};

In the preceding example, the abstract class demonstrates a chaotic design. The design is chaotic as it seems to represent many things, such as employee, address, and contact. One of the ways in which the preceding abstract class can be refactored is by breaking the single interface into three separate interfaces: IEmployee, IAddress, and IContact. In C++, interfaces are nothing but abstract classes with pure virtual functions:

#include <iostream>
#include <string>
#include <list>
using namespace std;

class IEmployee {
  private:
     string firstName, middleName, lastName,
     string title;
     string employeeCode;
     list<IAddress> addresses;
     list<IContact> contactNumbers;
  public:
     virtual string getAddress() = 0;
     virtual string getContactNumber() = 0;
};

class IAddress {
     private:
          string doorNo, street, city, pinCode, state, country;
     public:
          IAddress ( string doorNo, string street, string city, 
            string pinCode, string state, string country );
          virtual string getAddress() = 0;
};

class IContact {
      private:
           string countryCode, mobileNumber;
      public:
           IContact ( string countryCode, string mobileNumber );
           virtual string getMobileNumber() = 0;
};

In the refactored code snippet, every interface represents exactly one object, hence it is in compliance with the interface segregation design principle.