C-language advanced--enum, sizeof, typedef analysis 11

How to use enumeration types:

• Enum is a custom type of C language
• An enum value is an integer value that can be customized as needed
• The value of the first enum defaults to 0
• By default, the enum value is based on the previous defined value plus 1
• A variable of enum type can only be defined when the discrete value

1 enum Color 2 {  3    GREEN,  4    BLUE,  5    RED  6 }; 7 8 enum Color C = GREEN; 9 Ten printf ("%d\n", c);

Special meanings of enum types:

• The values defined in the enum are constants of the true meaning of the C language
• Enum is used in engineering to define integer constants

1 enum   //Nameless enumeration, used to define constants2 {3Array_size =Ten,//to define the size of an array4 };5 6 intArray[array_size] = {0};7 intI=0;8  for(i=0; i<array_size;i++)9 {Tenayyay[i]=i+1; One}

Sample Analysis:

1#include <stdio.h>2 3 enum4 {5Array_size =Ten6 };7 8 enumColor9 {TenRED =0x00ff0000, OneGREEN =0x0000FF00, ABLUE =0x000000ff - }; -  the voidPrintcolor (enumColor c) - { -     Switch(c) -     { +          CaseRED: -printf"color:red (0x%08X) \ n", c); +              Break; A          CaseGREEN: atprintf"color:green (0x%08X) \ n", c); -              Break; -          CaseBLUE: -printf"color:blue (0x%08X) \ n", c); -              Break; -     } in } -  to voidInitarray (intarray[]) + { -     inti =0; the      *      for(i=0; i<array_size; i++) $     {Panax NotoginsengArray[i] = i +1; -     } the } +  A voidPrintArray (intarray[]) the { +     inti =0; -      $      for(i=0; i<array_size; i++) $     { -printf"%d\n", Array[i]); -     } the } - Wuyi  the intMain () - { Wu     enumColor C =GREEN; -      About     intArray[array_size] = {0}; $      - Printcolor (c); -      - Initarray (array); A      + PrintArray (array); the      -     return 0; $}

Usage of the sizeof keyword:

• sizeof is the compiler's built-in indicator
• sizeof is used to calculate the size of the memory that the type or variable occupies
• The value of sizeof is determined at compile time

sizeof is used for type:

sizeof (type)

sizeof is used for variables:

sizeof (VAR) or sizeof Var--This non-parenthesized usage can fully illustrate that sizeof is not a function

sizeof is a C language built-in keyword instead of a function

• All sizeof will be replaced by specific values during the compilation process.
• The procedure does not have any relationship with sizeof.

Think about what the following program will output?

int var = 0;

int size = sizeof (var++);

printf ("var =%d, size =%d\n", var,size);

Example:

1#include <stdio.h>2 3 intf ()4 {5printf"Delphi tang\n");6     7     return 0;8 }9 Ten intMain () One { A     int var=0; -      -     intSize =sizeof(var++); the      -printf"var =%d, size =%d\n",var, size); -      -Size =sizeof(f ()); +      -printf"size =%d\n", size); +      A     return 0; at}

The output may be a bit unexpected because sizeof was replaced during compilation, so it will not participate in the run-time

Simulate a scene below

During the interview .....

Interviewer: Can you talk about the specific meaning of typedef?

Candidate: TypeDef is used to define a new type ...

Examiner: You go home and farm!

The meaning of typedef

• typedef is used to rename an already existing data type
• A typedef cannot essentially produce new types
• typedef rename Type 1. You can define 2 after a typedef statement. cannot be modified by unsigned and signed
• usage typedef type NEW_NAME

Example:

1#include <stdio.h>2 3typedefintInt32;4 5 struct_tag_point6 {7     intx;8     inty;9 };Ten  Onetypedefstruct_tag_point Point; A  -typedefstruct - { the     intlength; -     intarray[]; - } Softarray;  -  +typedefstruct_tag_list_node ListNode; - struct_tag_list_node + { Alistnode*Next; at }; -  - intMain () - { -Int32 i =- -;//int -     //unsigned Int32 II = 0; inPoint P;//struct _tag_point -softarray* SA =NULL;  tolistnode* node = NULL;//struct _tag_list_node* +      -     return 0; the}

Summary:

• The type of enum used for the discrete value of D-meaning
• The value defined by the enum is a constant in the true sense
• sizeof is the compiler's built-in indicator
• sizeof does not participate in the execution process of the program
• A typedef is used to rename a type, and a renamed type can be defined after a typedef statement

C-language advanced--enum, sizeof, typedef analysis 11