C foundation in-depth study I

C# Basic in-depth learning 01

Value type , Reference type

Data of value type is stored in the stack of memory , Data of reference type is stored in the heap of memory , The memory unit only stores the address of the object in the heap .

Value type variables directly store the actual data , Variables of reference type store the address of data , That is, the reference to the object .

Value type variables store the value of a variable directly on the stack , Reference type variables store the address of the actual data on the stack , The actual data is stored in the heap .

The value type represents the actual data , The reference type represents a pointer or reference to data stored in the memory heap .

Array

Array Attributes of a class

The following table lists them Array Some of the most commonly used properties in the class ：

Serial number	attribute & describe
1	IsFixedSize Get a value , This value indicates whether the array has a fixed size .
2	IsReadOnly Get a value , This value indicates whether the array is read-only .
3	Length Get one 32 An integer , This value represents the total number of elements in the array of all dimensions .
4	LongLength Get one 64 An integer , This value represents the total number of elements in the array of all dimensions .
5	Rank Get the rank of the array （ dimension ）.

If you need to know Array A complete list of properties of the class , See Microsoft's C# file .

Array Class method

The following table lists them Array Some of the most commonly used methods in classes ：

Serial number	Method & describe
1	Clear Depending on the type of element , Set the element of a range in the array to zero 、 by false Or for null.
2	Copy(Array, Array, Int32) Starting from the first element of the array, copy the elements of a range to the first element position of another array . The length consists of a 32 Bit integers specify .
3	CopyTo(Array, Int32) Copies all elements from the current one-dimensional array to the specified index position of a specified one-dimensional array . The index consists of a 32 Bit integers specify .
4	GetLength Get one 32 An integer , This value represents the total number of elements in the array of the specified dimension .
5	GetLongLength Get one 64 An integer , This value represents the total number of elements in the array of the specified dimension .
6	GetLowerBound Gets the lower bound of the specified dimension in the array .
7	GetType Gets the type of the current instance . From object （Object） Inherit .
8	GetUpperBound Gets the upper bound of the specified dimension in the array .
9	GetValue(Int32) Gets the value of a specified position in a one-dimensional array . The index consists of a 32 Bit integers specify .
10	IndexOf(Array, Object) Search for the specified object , Returns the first occurrence of the index in the entire one-dimensional array .
11	Reverse(Array) Reverse the order of elements in an entire one-dimensional array .
12	SetValue(Object, Int32) Sets the value of the element at the specified position in the one-dimensional array . The index consists of a 32 Bit integers specify .
13	Sort(Array) Use the... Of each element of the array IComparable Implement to sort the elements of the entire one-dimensional array .
14	ToString Returns a string representing the current object . From object （Object） Inherit .

params keyword

When using arrays as formal parameters ,C# Provides params keyword , When calling a method that takes an array as a parameter , You can pass array arguments , You can also pass a set of array elements .params The format used is ：

public  Return type   Method name ( params  Type the name []  Array name  )

Structure （Struct）

stay C# in , A structure is a value type data structure . It enables a single variable to store related data of various data types .struct Keyword is used to create a structure .

Structural characteristics

You have used a simple name Books Structure . stay C# The structure in is different from the traditional C or C++ The structure in is different .C# The structure in has the following characteristics ：

• The structure can have methods 、 Field 、 Indexes 、 attribute 、 Operators, methods, and events .
• Structure defines a constructor , But you can't define destructors . however , You cannot define a parameterless constructor for a structure . Parameter free constructor ( Default ) Is automatically defined , And cannot be changed .
• Different from class , Structure cannot inherit other structures or classes .
• Structure cannot be used as the infrastructure of other structures or classes .
• Structure can implement one or more interfaces .
• Structure member cannot be specified as abstract、virtual or protected.
• When you use New When the operator creates a structure object , The appropriate constructor will be called to create the structure . Different from class , The structure may not use New Operators can be instantiated .
• If not used New The operator , Only after all fields have been initialized , The field is assigned , Objects are used .

class vs structure

Classes and structures have the following basic differences ：

• Class is a reference type , A structure is a value type .
• Structure does not support inheritance .
• Structure cannot declare a default constructor .
• In the constructor of a struct , All fields of the structure must be assigned , Class constructor has no such restriction .
• A field declared in a structure cannot be given an initial value , Classes can be .