Difference Between Structure and Class in C++
In C++, a structure works the same way as a class, except for just two small differences. The most important of them is hiding implementation details. A structure will by default not hide its implementation details from whoever uses it in code, while a class by default hides all its implementation details and will therefore by default prevent the programmer from accessing them. The following table summarizes all of the fundamental differences.
Class
|
Structure
|
1. Members of a class are private by default. |
1. Members of a structure are public by default. |
2. An instance of a class is called an ‘object’. |
2. An instance of structure is called the ‘structure variable’. |
3. Member classes/structures of a class are private by default but not all programming languages have this default behavior eg Java etc. |
3. Member classes/structures of a structure are public by default. |
4. It is declared using the class keyword. |
4. It is declared using the struct keyword. |
5. It is normally used for data abstraction and further inheritance. |
5. It is normally used for the grouping of data |
6. NULL values are possible in Class. |
6. NULL values are not possible. |
7. Syntax:
class class_name{
data_member;
member_function;
};
|
7. Syntax:
struct structure_name{
type structure_member1;
type structure_member2;
};
|
Some examples that elaborate on these differences:
1) Members of a class are private by default and members of a structure are public by default.
For example, program 1 fails in compilation but program 2 works fine,
Program 1:
C++
#include <iostream>
using namespace std;
class Test {
int x;
};
int main()
{
Test t;
t.x = 20;
return t.x;
}
|
Time Complexity: O(1)
Auxiliary Space: O(1)
Output:
./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp: In function 'int main()':
./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp:10:9: error: 'int Test::x' is private
int x;
^
./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp:18:7: error: within this context
t.x = 20;
^
./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp:10:9: error: 'int Test::x' is private
int x;
^
./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp:20:14: error: within this context
return t.x;
^
Program 2:
C++
#include <iostream>
using namespace std;
struct Test {
int x;
};
int main()
{
Test t;
t.x = 20;
cout << t.x;
}
|
Time Complexity: O(1)
Auxiliary Space: O(1)
2) A class is declared using the class keyword, and a structure is declared using the struct keyword.
Syntax:
class ClassName {
private:
member1;
member2;
public:
member3;
.
.
memberN;
};
Syntax:
struct StructureName {
member1;
member2;
.
.
.
memberN;
};
3) Inheritance is possible with classes, and with structures
For example, programs 3 and 4 work fine.
Program 3:
C++
#include <iostream>
using namespace std;
class Parent {
public :
int x;
};
class Child : public Parent {
public :
int y;
};
int main()
{
Child obj1;
obj1.y = 7;
obj1.x = 91;
cout << obj1.y << endl;
cout << obj1.x << endl;
return 0;
}
|
Time Complexity: O(1)
Auxiliary Space: O(1)
Program 4:
C++
#include <iostream>
using namespace std;
struct Base {
public :
int x;
};
struct Derived : Base {
public :
int y;
};
int main()
{
Derived d;
d.x = 20;
cout << d.x;
cin.get();
return 0;
}
|
Output
20
Time Complexity: O(1)
Auxiliary Space: O(1)
To know about the Difference between C structures and C++ structures refer to this article.
Last Updated :
22 Apr, 2023
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