【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

#include <stdio.h>

typedef int MyInt;
typedef MyInt MyInt2;

// 给指针类型char *起一个新的类型名称String
typedef char * String;

/*
struct Student
{
    int age;
};
typedef struct Student MyStu;
*/

/*
typedef  struct Student
{
    int age;
} MyStu;
*/


typedef struct
{
    int age;
} MyStu;

/*
enum Sex {Man, Woman};
typedef enum Sex MySex;
*/

typedef enum {
    Man,
    Woman
} MySex;


typedef int (*MyPoint)(int, int);

int minus(int a, int b)
{
    return a - b;
}

int sum(int a, int b)
{
    return a + b;
}
/*
struct Person
{
    int age;
};

typedef struct Person * PersonPoint;
*/

typedef struct Person
{
    int age;
} * PersonPoint;

int main()
{
    // 定义结构体变量
    struct Person p = {20};
    
    PersonPoint p2 = &p;
    
    //struct Person *p2 = &p;
    
    //MyPoint p = sum;
    //MyPoint p2 = minus;
    //int (*p)(int, int) = sum;
    
    //int (*p2)(int, int) = minus;
    
    //p(10, 11);
    
    
    //MySex s = Man;
    //enum Sex s = Man;
    //enum Sex s2 = Woman;
    
   // struct Student stu3;
    //MyStu stu = {20};
    //MyStu stu2= {21};
    
    return 0;
}

void test2()
{
    String name = "jack";
    
    printf("%s
", name);
}

void test()
{
    int a;
    MyInt i = 10;
    MyInt2 c = 20;
    
    MyInt b1, b2;
    
    printf("c is %d
", c);
}

使用注意

#include <stdio.h>

//#define Integer int

//typedef int Integer;

//typedef unsigned long int MyInt;

#define String2 char *

typedef char * String;

int main()
{
    /*
    int a,b;
    int a;
    int b;
    */
    
    //s1、s2是char *指针
    String s1, s2;
    /*
     String s1;
     String s2;
     */
    s1 = "jack";
    s2 = "rose";
    
    // s3才是char *指针，s4只是char
    String2 s3, s4;
    /*
    char *s3, s4;
    char *s3;
    char s4;
    */
    //String2 s3 = "jake";
    
    /*
    String s1;
    String s2;
    */
    
    
    
    
    //Integer i = 10;
    
    return 0;
}