C and pointer Chapter 3-Data

Overview:

Chapter 3 of C and pointer describes the data.

This section mainly describes three attributes of a variable: scope, link property, and storage type.

These three attributes determine where the variable can be used and how long the value of the variable remains ".

 

Summary scope:

1. File Scope, code block scope, prototype scope, and function Scope

File Scope: The identifier File Scope declared outside the code block

Code block scope: declared in {}

Prototype scope: int getscore (INT ucstudent); in this function prototype declaration, int ucstudent has the prototype scope.

Function scope: Skip this.

Summary Link Attributes:

Link Attributes: external (external link attributes), internal (internal Link Attributes), and none (without Link Attributes)

Functions of Link Attributes: The Link property of the identifier determines how the identifier appears in different source files.

For example, the same identifier A appears in different source files. When these source files are compiled to form the target file,

When the next link is used to form an executable file, a indicates whether the same object is a different object, which is determined by the link attribute of.

External: an identifier with an external link attribute. No matter how many times it is declared, the object is the same regardless of the source file.

Internal: When a has the intonernal link attribute, the declaration in the same source file points to the same entity, and multiple declarations in different source files belong to different entities.

None: the declarations of the same or different source files point to different entities.

1. All variables with file scopes are "external Link Attributes" by default"

2. The variable declared in the function or code block is "NONE" by default.

3. Static and extern can change the link attribute of the identifier, but they have the following restrictions:

1) static: only declarations with the default external attribute change.

2) When the extern keyword is used for the first declaration of an identifier in the source file, it has the effect of modifying the link attribute, but is used for the second or later Declaration of the identifier

The link attribute declared for the first time will not be changed.

Summary Storage types

Storage type refers to the memory type in which the variable value is stored.

Static	Normal memory	Global variables, static global variables, and static local variables
Automatic Storage Type	Stored in the stack	Local variable
Register	Stored in registers	Variable modified by the register keyword

C and pointer Chapter 3-Data