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Let's discuss, what are the differences between structures in C and structures in C++? In C++, structures are similar to classes.
C Structures | C++ Structures |
|---|---|
| Only data members are allowed, it cannot have member functions. | Can hold both: member functions and data members. |
| Cannot have static members. | Can have static members. |
| Cannot have a constructor inside a structure. | Constructor creation is allowed. |
| Direct Initialization of data members is not possible. | Direct Initialization of data members is possible. |
| Writing the ‘struct’ keyword is necessary to declare structure-type variables. | Writing the ‘struct’ keyword is not necessary to declare structure-type variables. |
| Do not have access modifiers. | Supports access modifiers. |
| Only pointers to structs are allowed. | Can have both pointers and references to the struct. |
| Sizeof operator will generate 0 for an empty structure. | Sizeof operator will generate 1 for an empty structure. |
| Data Hiding is not possible. | Data Hiding is possible. |
Similarities Between the C and C++ Structures
Lets discuss some of the above mentioned differences and similarities one by one:
1. Member functions inside the structure: Structures in C cannot have member functions inside a structure but Structures in C++ can have member functions along with data members.
Output
This will generate an error in C but no error in C++.
num=9
2. Static Members: C structures cannot have static members but are allowed in C++.
This will generate an error in C but not in C++.
3. Constructor creation in structure: Structures in C cannot have a constructor inside a structure but Structures in C++ can have Constructor creation.
This will generate an error in C.
Output in C++:
2
4. Direct Initialization: We cannot directly initialize structure data members in C but we can do it in C++.
This will generate an error in C.
Output in C++:
7
5. Using struct keyword: In C, we need to use a struct to declare a struct variable. In C++, a 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.
6. 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.
7. Pointers and References: In C++, there can be both pointers and references to a struct in C++, but only pointers to structs are allowed in C.
8. sizeof operator: This operator will generate 0 for an empty structure in C whereas 1 for an empty structure in C++.
Output in C:
0
Output in C++:
1
NOTE: The default type of sizeof is long unsigned int , that's why "%lu" is used instead of "%d" in printf function.
9. Data Hiding: C structures do not allow the concept of Data hiding but are permitted in C++ as it is an object-oriented language whereas C is not.
10. Constant Members: C struct may allow to declare constant members, but no way to initialize. But in C++, you can initialize using constructor initializer list
Output in C:
Struct with constant members, but how to init??
Output in C++:
Struct with constant members: 2 3
Related Article: Structure vs Class in C++
