教學用的投影片。關於C#的Struct和Class的差異，做個說明。

1. C#
Struct & Class
2013,11
by aecho

2. References
Dot Net Book Zero
http://www.charlespetzold.com/dotnet/
Author, Charles Petzold

3. Mantra
Struct is Value type; Class is Reference type.

4. Outlines
The way of allocating memory block.
New operation
Equality about “==“ and Equals().

5. Struct
The primitive data types
int, short, double, long, …
DateTime struct, Guid struct, and …
custom defined struct types
struct A { …. }

6. Class
string class.
custom defined class types.
class A { …. }

7. Stack
int i = 10;
MyClass a =
new MyClass();
MyClass b = a;
i
10
a
0x01
b
0x01
Heap
0x01
…

8. Stack
int i = 10;
DateTime now =
i
DateTime.Now;
Guid id =
Guid.NewGuid();
now
id
10
2013/10/31
12:00:00
“382c74c3-721d
-4f34-57657b6
cbc27”

9. Stack
Heap
string a = “Hello
World”;
int b[] = new int[]
a
0x01
0x01
b
0x02
0x02
“Hello
World”
{1,2,3};
{1, 2, 3}

10. New operator
New() will call parameterless constructor in
struct or class.
new DateTime(), new Guid(),
new Contact()

11. New operator
For struct
Default parameterless constructor.
Always have one.
Initialize all fields to 0 or null.
Can’t be customized.

12. New operator
A struct example.

13. New operator
For class
Default parameterless constructor.
If no constructor defined, compiler will
create one.
Could be customized.

14. New operator
•
PointClass
•
•
Customized parameterless
constructor.
RectClass
•
A parameterless constructor will
•
It initialized all field to 0 or null.
be created by compiler.

15. New operator
•
As for Cat class
•
No parameterless constructor
•
Only Cat(string aName)
will be created.
constructor can be used.

16. Equality
“==” vs “Equals()”

17. A == B? A.Equals(B)?
For struct,
A == B,
depend on the implementations of
operators “==” and “!=”.
A.Equals(B),
T
rue, If all fields of A and B are equal.

18. A == B? A.Equals(B)?
Stack
pt_1
pt_2
Equals() is T
rue, if all fields are
the same in struct.
x = 3
y=5
x=3
y=5

19. A == B? A.Equals(B)?
For class,
A == B
T
rue, if they point to the same heap memory address.
A.Equals(B)
Depends on the implementations of Equals().
Equals() of System.Object class
Compare memory addresses.

20. A == B? A.Equals(B)?
Stack
pt_1 0x01
pt_2 0x02
pt_3 0x01
Heap
0x01
0x02
x = 3
y=5
x=3
y=5

21. Examples
What is b2 ?

22. == vs Equals()
Conclusions about Equality,
Compare equality of objects.
Equals()
Compare the memory addresses.
== operator

23. Any question ?