C Language Learning notes--type definition & Union

• First, type definition

C-Language custom data type (typedef)

　　　　The C language provides a function called TypeDef to declare a new name for an existing data type.

typedef int LENGTH;

Makes Length an alias of type int .

In this way, the length can be substituted for int appearing in defining variables and declaring functions where.

Length A, B;

Length A[10];

　　The name of the new type is the alias of the original type, which improves the readability of the program.

typedef struct {

int day;

int month;

int year;

} Date; Declares a struct type whose alias is date

• Ii. United

Store

All the members share a space.

Only one member is valid at the same time.

The size of the Union is its largest member.

Initialization

　　Initializes the first member of a

Union anelt{

int i;

char c;

} anelt1,anelt2;

sizeof (Union ...) sizeof Maximum value per member

　　　　

      1#include <stdio.h>2       3typedef Union {4         inti; 5         Charch[sizeof(int)]; 6} CHI; 7       8 intMainintGrcConst Char*grv[])9 {     TenChi, Chi;  One         inti;  ACHI.I =1234;  -          for(i=0; i<sizeof(int) ; i++){      -printf"%02HHX", Chi.ch[i]);  the         }      -printf"\ n");  -       -         return 0;  +}

C Language Learning notes--type definition & Union