Structure vs class in C++

Difficulty Level : Easy
Last Updated : 11 Jul, 2019

In C++, a structure is the same as a class except for a few differences. The most important of them is security. A Structure is not secure and cannot hide its implementation details from the end user while a class is secure and can hide its programming and designing details. Following are the points that expound on this difference:

1) Members of a class are private by default and members of a struct are public by default.
For example program 1 fails in compilation and program 2 works fine.

   
// Program 1 
#include <stdio.h> 
  
class Test { 
    int x; // x is private 
}; 
int main() 
{ 
  Test t; 
  t.x = 20; // compiler error because x is private 
  getchar(); 
  return 0; 
} 

   
// Program 2 
#include <stdio.h> 
  
struct Test { 
    int x; // x is public 
}; 
int main() 
{ 
  Test t; 
  t.x = 20; // works fine because x is public 
  getchar(); 
  return 0; 
} 

2) When deriving a struct from a class/struct, default access-specifier for a base class/struct is public. And when deriving a class, default access specifier is private.
For example program 3 fails in compilation and program 4 works fine.

   
// Program 3 
#include <stdio.h> 
  
class Base { 
public: 
    int x; 
}; 
  
class Derived : Base { }; // is equilalent to class Derived : private Base {} 
  
int main() 
{ 
  Derived d; 
  d.x = 20; // compiler error becuase inheritance is private 
  getchar(); 
  return 0; 
} 

   
// Program 4 
#include <stdio.h> 
  
class Base { 
public: 
    int x; 
}; 
  
struct Derived : Base { }; // is equilalent to struct Derived : public Base {} 
  
int main() 
{ 
  Derived d; 
  d.x = 20; // works fine becuase inheritance is public 
  getchar(); 
  return 0; 
} 

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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