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

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   // 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': */

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   C++

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   // 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

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   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

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   // 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;      ^*/

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   C++

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   // C++ program with structure static member    struct Record {     static int x; };    // Driver program int main() {     return 0; }

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   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

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   // 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': */

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   C++

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   // 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

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   Output:

   2

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

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   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.

Related Article: Structure vs Class in C++

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