Using typedef in C language to change the name of data type

typedef keyword

In addition to direct use C The name of the data type provided by the language （ Such as int,char,float,double etc. ） And the structure type name defined by ourselves , You can also use typedef Specify a new data type name to replace the existing type name . let me put it another way ,typedef Is that Alias existing data types . for example ：

#include <stdio.h>

typedef int Integer; //  to int Took a person named Integer, You can use Integer To define shaping variables 
typedef char * String; //  to char * Took a person named String, You can use String To define character pointer variables 

int main()
{
    
	Integer i = 10; //  Equate to  int i = 10;
	String p; //  Equate to  char * p;

	return 0;
}

#include <stdio.h>

typedef struct Student
{
    
	char name[100];
	int age;
	float score;
}ST, * PST; //  to  struct Student  It's a nickname ST, to  struct Student *  A man named PST

int main()
{
    
	ST stu;		//  Equate to  struct Student stu;
	PST pStu;	//  Equate to  ST * pStu;  Also equivalent to  struct Student * pStu;

	return 0;
}

It should be noted that ,C The original structure name and use are allowed in the language typedef The renamed structure has the same name , for example ：

#include <stdio.h>

typedef struct Student
{
    
	char name[100];
	int age;
	float score;
}Student; //  At this time  Student  Is equivalent to  struct Student

int main()
{
    
	Student stu;	//  Equate to  struct Student stu;
	
	return 0;
}

• Why rename data types ？
• The first is to facilitate programmer programming , For example, when we define structural variables , If you always have to write first struct Then write the structure name , Defining structural variables becomes very tedious , Write it every time struct, And it's easy to forget to write code , And the code will be cumbersome , If we can use a few short letters to represent a long structure name , Then why don't we do it ？
• The second is the universality of the whole program , If the variables that a program initially stores data are integers , What is naturally defined in the program are integer variables , But if you want to change all defined data variables to floating-point type at some time , The workload is predictable , But there are typedef To help. , It only takes one step to finish . Because the first thing we want to store is integer data , Then we can put int Rename it as ElemType（ Of course, you can choose any name , Here we take ElemType It's just convenient to use in data structure ）, namely ,typedef int ElemType;, When we want to change the variables corresponding to these data to floating point , We just need to do this typedef float ElemType;, Compared with modifying the types of variables one by one , Use typedef It's really easy ！
• There's more , In order to achieve Code is comment Purpose , Great programmers often rename data types .
• If you don't quite understand why this is the case , You can leave an impression in your mind first , Come back and analyze it carefully when you need to use this part , You can knock more and watch more , In fact, in the process of programming, you will gradually understand the benefits of doing so .