Fundamentals of C language

Preface

For those used in work C Language grammar , Part of the content comes from the reference blog .

Not specializing in the software industry , Code is only the foundation to meet functional requirements . Update and enrich the content in the later stage .

1 grammar

1.1 Structure

-> It's a whole , It is used to point to the structure 、C++ Medium class And other pointers containing sub data are used to get sub data . In other words , If we were C Language defines a structure , Then declare a pointer to the structure , Then we need to use the pointer to get the data in the structure , You use “->”

struct Data
{
   int a,b,c;
};              /* Defining structure */
struct Data * p;/* Define structure pointer */
struct Data A = {1,2,3};/* Declare variables A*/
int x;/* Declare a variable x*/
p = &A ; /* Give Way p Point to A*/
x = p->a;/* This sentence means to take out p Data items contained in the pointed structure a Assign a value to x*/
         /* Because of this time p Point to A, thus  p->a == A.a, That is to say 1*/

 For the first question  p = p->next; This should appear in C Linked list of languages , there next It should be one with p Structure pointer of the same type , Its definition format should be ：
struct Data 
{
   int a;
   struct Data * next;
};/* Defining structure */
…………
main()
{
   struct Data * p;/* Declare pointer variables p*/
  ……
   p = p->next;/* take next The value in is assigned to p*/
}

1.2 Register sheet bit operation

take 32bit Bit wide register GPIOx_CRL A certain bit ( The first n bit , n from 0 start ) Set up 1, Take measures ：

GPIOx_CRL = GPIOx_CRL | (0x01 << n)    //n from 0 Start 
GPIOx_CRL = GPIOx_CRL | (0x01 << 0)    // take GPIOx_CRL[0] Set up 1
GPIOx_CRL = GPIOx_CRL | (0x01 << 3)    // take GPIOx_CRL[3] Set up 1

take 32bit Bit wide register GPIOx_CRL A certain bit ( The first n bit , n from 0 start ) Set up 0, Take measures ：

GPIOx_CRL = GPIOx_CRL & (~(1 << n))  	/*  Clear the ground n bit position  */

// analysis , if GPIOx_CRL = 1001 1111,n=2,
(1<<2)  Get the binary number ：0000 0100
 Reverse is ：1111 1011
GPIOx_CRL = (1001 1111) & (1111 1011) = 1001 1011

1.3 There are many registers bit assignment

take 32bit Bit wide register GPIOx_CRL Medium bit[6:2] Assign a new value , You need to first put this bit[6:2] Zero clearing , Then assign a value . Steps are as follows ：

// Reference code --------------------------------------------------------
// First , take GPIOx_CRL[6:2] Zero clearing . Clear the zero table bit Just a few bit Of 1 Move left and reverse 、 Then with the original register value  “ Meet each other ”
GPIOx_CRL = GPIOx_CRL & (~(0x1f << 2))  	/*  Clear the ground [6:2] bit position  */
// secondly , take GPIOx_CRL[6:2] Assign new values to "0xd" , Just move the new value to the left 、 With the original value “ Phase or ”
GPIOx_CRL = GPIOx_CRL | (0xd << 2)


// Code parsing --------------------------------------------------------
// if GPIOx_CRL = 1001 1111, The clearing steps are as follows ：
(0x1f<<2)  Get the binary number ：0111 1100
 Reverse is               ：1000 0011
GPIOx_CRL = (1001 1111) & (1000 0011) = 1000 0011

// assignment 
0xd  Binary is         ：1101
(0xd << 2) yes         ：110100
GPIOx_CRL = GPIOx_CRL | (0xd << 2) = 1000 0011 | 11 0100 =1011 0111

give an example , Put the following register bit0 Set up 1, All functional segments of this register can be completed Declaration definition , Then use the following method

GPIOx_CRL = GPIOx_CRL | (0x01 << BLOCK_COUNT_ENABLE) // take GPIOx_CRL.BLOCK_COUNT_ENABLE Set up 1

  Here we need to pay attention to , The above operation is in the register BLOCK_COUNT_ENABLE The seat width is 1bit

If necessary AUTO_CMD_ENABLE Modify its value , Like this 2bit The original value is 0x3, If it needs to be modified to 0x1, The following expression may have problems

GPIOx_CRL = GPIOx_CRL | (0x01 << AUTO_CMD_ENABLE) //

therefore , If you need to register some bit Field assignment , You can consider these first bit Zero clearing , Then assign a value .

for example , You need to set the second 0 position bit=1 when , It cannot be simply set to ：GPIOx_CRL=0x01  , Such a method will make the low configuration register GPIOx_CRL All other bits of are set to 0.

  For binary operations ：  

No matter the original value of this bit is 0 still 1, It goes with 0 Conduct & operation , All the results are 0, And follow 1 Conduct & operation , The original value will remain the same ;  

No matter the original value of this bit is 0 still 1, It goes with 1 Conduct | operation , All the results are 1, And follow 0 Conduct | operation , The original value will remain the same . 

Common grammar

 1、if else grammar 

    if(age>=18){
        printf(" Congratulations , You are an adult , You can use the software ！\n");
    }else{
        printf(" I'm sorry , You're underage , It is not suitable to use this software ！\n");
    }

2、while grammar 
#include <stdio.h>
int main(void){
    int i,sum=0;
    i=1;
    while(i<=100){
        sum=sum+i;
        i++;
    }
    printf("%d\n",sum);
    return 0;
}


#include <stdio.h>
int main(void){
    int n=0;
    printf("input a string:\n");
    while(getchar()!='\n') n++;
    printf("%d",n);
    return 0;
}



3、 Function definition and use 

 

 

Reference resources

1、 author	post
	【 turn 】C In language -＞ What does that mean? ？
	C Language bit operation - bit 、byte Zero clearing , Set up 1, extract , Judge
	C Language bit operations on registers