[Learning notes] [C Language] typedef, learning notes typedef

[Learning notes] [C Language] typedef, learning notes typedef

1. Concept

We can use the typedef keyword to define a new name (alias) for various data types ).

2. Role: Create a new name for an existing type

3. Application scenarios:
1> Basic Data Type
2> pointer
3> struct
4> Enumeration
5> pointer to function

4. Code

1 # include <stdio. h> 2 3 typedef int MyInt; 4 typedef MyInt MyInt2; 5 6 // a new type name String 7 typedef char * String for the pointer type char; 8 9/* 10 struct Student 11 {12 int age; 13}; 14 typedef struct Student MyStu; 15 */16 17/* 18 typedef struct Student 19 {20 int age; 21} MyStu; 22 */23 24 25 typedef struct 26 {27 int age; 28} MyStu; 29 30/* 31 enum Sex {Man, Woman }; 32 typedef enum Sex MySex; 33 */34 35 typedef enum {36 Man, 37 Woman 38} MySex; 39 40 41 typedef int (* MyPoint) (int, int ); 42 43 int minus (int a, int B) 44 {45 return a-B; 46} 47 48 int sum (int a, int B) 49 {50 return a + B; 51} 52/* 53 struct Person 54 {55 int age; 56}; 57 58 typedef struct Person * PersonPoint; 59 */60 61 typedef struct Person 62 {63 int age; 64} * PersonPoint; 65 66 int main () 67 {68 // define struct variable 69 struct Person p = {20}; 70 71 PersonPoint p2 = & p; 72 73 // struct Person * p2 = & p; 74 75 // MyPoint p = sum; 76 // MyPoint p2 = minus; 77 // int (* p) (int, int) = sum; 78 79 // int (* p2) (int, int) = minus; 80 81 // p (10, 11 ); 82 83 84 // MySex s = Man; 85 // enum Sex s = Man; 86 // enum Sex s2 = Woman; 87 88 // struct Student stu3; 89 // MyStu stu = {20}; 90 // MyStu stu2 = {21}; 91 92 return 0; 93} 94 95 void test2 () 96 {97 String name = "jack"; 98 99 printf ("% s \ n", name); 100} 101 102 void test () 103 {104 int; 105 MyInt I = 10; 106 MyInt2 c = 20; 107 108 MyInt b1, b2; 109 110 printf ("c is % d \ n", c); 111}

Usage notes

1 # include <stdio. h> 2 3 // # define Integer int 4 5 // typedef int Integer; 6 7 // typedef unsigned long int MyInt; 8 9 # define String2 char * 10 11 typedef char * String; 12 13 int main () 14 {15/* 16 int a, B; 17 int a; 18 int B; 19 */20 21 // s1 and s2 are char * pointers 22 String s1, s2; 23/* 24 String s1; 25 String s2; 26 */27 s1 = "jack"; 28 s2 = "rose"; 29 30 // s3 is the char * pointer, s4 is only char31 String2 s3, s4; 32/* 33 char * s3, s4; 34 char * s3; 35 char s4; 36 */37 // String2 s3 = "jake"; 38 39/* 40 String s1; 41 String s2; 42 */43 44 45 46 47 // Integer I = 10; 48 49 return 0; 50}