Part C - value types and reference types

1. Value type and Reference type （ contrast ）

Value type ：	byte,short,int,long,float,double,decimal,char,bool and struct Collectively referred to as value types .
Reference type ：	string and class Collectively referred to as reference types .

Concept ： Value types store their values directly （ Represents actual data ）, Reference types store references to their values （ Express Points to... Stored in the memory heap Pointers and references to data ）

Base class ： Value types are implicitly derived from System.ValueType, The reference type base class is Object

Storage ： The value type is stored in the memory stack , Fast access , Stack memory is automatically released ;

            Data of reference type is stored in memory heap , The memory unit stores the address stored in the heap , Slow access , Heap memory is .Net Species GC( Garbage collection mechanism ） To automatically release

premium ：

• After value type variable declaration , Whether assigned or not , The compiler allocates memory for it .
• Reference type when declaring a class , Only a small piece of memory is allocated in the stack to accommodate an address , At this time, there is no memory space allocated on the heap . When using new When creating an instance of a class , Allocate space on the heap , And save the address of the space on the heap to the small space allocated on the stack .
• Instances of value types are usually allocated on the thread stack （ Static allocation ）, But in some cases it can be stored in the heap .
• Objects of reference type are always allocated in the process heap （ Dynamic allocation ）

• The amount of space allocated by the value type in the stack varies depending on the variable type ;

• The reference type has the same space in the stack ;

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