【学习笔记】【C语言】typedef

1.概念

我们可以使用typedef关键字为各种数据类型定义一个新名字(别名)。

2.作用：给已经存在的类型起一个新的名称

3.使用场合：
1> 基本数据类型
2> 指针
3> 结构体
4> 枚举
5> 指向函数的指针

4.代码

  1 #include <stdio.h>
  2 
  3 typedef int MyInt;
  4 typedef MyInt MyInt2;
  5 
  6 // 给指针类型char *起一个新的类型名称String
  7 typedef char * String;
  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     // 定义结构体变量
 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
", name);
100 }
101 
102 void test()
103 {
104     int a;
105     MyInt i = 10;
106     MyInt2 c = 20;
107     
108     MyInt b1, b2;
109     
110     printf("c is %d
", c);
111 }

使用注意

 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、s2是char *指针
22     String s1, s2;
23     /*
24      String s1;
25      String s2;
26      */
27     s1 = "jack";
28     s2 = "rose";
29     
30     // s3才是char *指针，s4只是char
31     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 }