Difference between C structures and C++ structures

In C++, struct and class are exactly the same things, except for that struct defaults to public visibility and class defaults to private visibility.
Some important differences between the C and C++ structures:

1. Member functions inside structure: Structures in C cannot have member functions inside structure but Structures in C++ can have member functions along with data members.
2. Direct Initialization: We cannot directly initialize structure data members in C but we can do it in C++.
   
   C

   // C program to demonstrate that direct
   // member initialization is not possible in C
   #include <stdio.h>
   
   struct Record {
       int x = 7;
   };
   
   // Driver Program
   int main()
   {
       struct Record s;
       printf("%d", s.x);
       return 0;
   }
   /* Output :  Compiler Error
      6:8: error: expected ':', ', ', ';', '}' or
     '__attribute__' before '=' token
     int x = 7;
           ^
     In function 'main': */

   C++

   // CPP program to initialize data member in c++
   #include <iostream>
   using namespace std;
   
   struct Record {
       int x = 7;
   };
   
   // Driver Program
   int main()
   {
       Record s;
       cout << s.x << endl;
       return 0;
   }
   // Output
   // 7
   
   Output:

   7

3. Using struct keyword: In C, we need to use struct to declare a struct variable. In C++, struct is not necessary. For example, let there be a structure for Record. In C, we must use “struct Record” for Record variables. In C++, we need not use struct and using ‘Record‘ only would work.
4. Static Members: C structures cannot have static members but is allowed in C++.
   
   C

   // C program with structure static member
   struct Record {
       static int x;
   };
   
   // Driver program
   int main()
   {
       return 0;
   }
   /* 6:5: error: expected specifier-qualifier-list
      before 'static'
        static int x;
        ^*/

   C++

   // C++ program with structure static member
   
   struct Record {
       static int x;
   };
   
   // Driver program
   int main()
   {
       return 0;
   }
   
   This will generate an error in C but no error in C++.
5. Constructor creation in structure: Structures in C cannot have constructor inside structure but Structures in C++ can have Constructor creation.
   
   C

   
   
   

   // C program to demonstrate that Constructor is not allowed
   #include <stdio.h>
   
   struct Student {
       int roll;
       Student(int x)
       {
           roll = x;
       }
   };
   
   // Driver Program
   int main()
   {
       struct Student s(2);
       printf("%d", s.x);
       return 0;
   }
   /* Output :  Compiler Error
      [Error] expected specifier-qualifier-list
       before 'Student'
      [Error] expected declaration specifiers or
      '...' before numeric constant
      [Error] 's' undeclared (first use
      5555555555in this function)
      In function 'main': */

   C++

   // CPP program to initialize data member in c++
   #include <iostream>
   using namespace std;
   
   struct Student {
       int roll;
       Student(int x)
       {
           roll = x;
       }
   };
   
   // Driver Program
   int main()
   {
       struct Student s(2);
       cout << s.roll;
       return 0;
   }
   // Output
   // 2
   
   Output:

   2

6. sizeof operator: This operator will generate 0 for an empty structure in C whereas 1 for an empty structure in C++.

   // C program to illustrate empty structure
   #include <stdio.h>
   
   // empty structure
   struct Record {
   };
   
   // Driver program
   int main()
   {
       struct Record s;
       printf("%d\n", sizeof(s));
       return 0;
   }

   Output in C:

   0
   

   Output in C++:

   1

7. Data Hiding: C structures do not allow concept of Data hiding but is permitted in C++ as C++ is an object oriented language whereas C is not.
8. Access Modifiers: C structures do not have access modifiers as these modifiers are not supported by the language. C++ structures can have this concept as it is inbuilt in the language.

This article is contributed by Shubham Chaudhary. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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