C Language-keyword typedef

1. Basic use

The use of 1> typedef in basic data types

typedef int MYINT; equals an alias to int.

typedef MYINT MYINT2; It's the equivalent of an alias for MyInt.

MyInt a = 10; Myint equivalent to int

MyInt2 B = 12; MyInt2 equivalent to int

2> typedef and pointers when used together

Char *name = "Jack";

typedef char * string;//equivalent to (char *) a name string

String name1 = "Jame";

3> the use of typedef and structs together

①struct Date {int year; int month; int day};

typedef struct DATE mydate;//is equivalent to an alias for struct date

②typedef truct Date {int year; int month, int day} mydate;//another way to use

③typedef truct {int year; int month, int day} mydate;//another way to use

4> typedef and enumeration when used together

Enum Sex {Sexman,sexwoman,unknow};

typedef enum SEX {Sexman,sexwoman,unknow} mysex;//is equivalent to an alias for an enumeration type

Mysex s = sexman;//defining variables

5> typedef and function pointers when used together

int sum (int a, int b)

{

return a + B;

}//first defines a function

Int (*p) (int, int);//defines a pointer type that points to a function

typedef int (*mypoint) (int, int);//Pointer to function the type of a name MyPoint

MyPoint p = sum;

6> typedef and struct pointers when used together

struct Date {int year; int month; int day};//defines a struct type

struct Date d = {1990, 10, 10};//defines struct-body variables

struct Date *p = &d;//defines a pointer to a struct variable

typedef struct DATE *datepoint;

Datepoint P2 = &d;

typedef struct DATE {int year; int month; int day} * dstepoint;//another way of defining

7> Summary

① function: A new name for an already existing type

② Use occasions:

1) Basic Data type

2) Structural body

3) pointer

4) enumeration

5) Pointer to function

2. Use note

1> typedef and macro definitions are used at the same time, note that the macro definition is text substitution

#denfine string2 char *

Type char * string;

String s1,s2; S1, S2 are all char * types

String2 S3,s4; S3 is a char * type, S4 is a char type, because the macro is a text substitution

C Language-keyword typedef