Preface

 I told you before  fputc  Not at all   Line cache   It was used while（1）; And join newline validation  
fputc and  fgetc  Configuration and use   Note that the cursor should be shifted back to the 0 A place  
 This section talks about cat  The principle of instruction  

cat Instruction Introduction

cat  Implementation process  

take a.C analogy

 The user reads from the kernel first   The user is writing to the kernel   Through the driver of the kernel   Output to the display  

getc/fputc Function coordination Realization cat Instructions

 use  man  Shape parameter   Just make it happen  

 I learned from the front  1 gets/puts 2 fgets/fputs 3 fgetc/fputc  Three groups of   Read and write functions 
 1  You can't   Because it can only be simple   Output   Input  

int argc： Indicates the number of parameters on the command line  
char *argv[]： The actual parameters are determined by the system when entering the command line   A total of three. 
 Now? cat  Count one   Don't write it in code  argv[0]
 because   The first is the fixed instruction   The latter two are the source file names   Or parameters  

#include<stdio.h>

int  main(int argc,char *argv[])
{
    
     FILE *fd;
     int str;
     if(argc!=2)// If it's not two parameters   It's the exception  cat xxx.C  It's just two parameters  
     {
    
         printf("fopen is error\n");
         return -1;
     }
     printf("fopen is success\n");
     fd=fopen(argv[1],"r");
    
     while(1) // Because I read and write more than once   So just loop  
     {
    
         Nret=fgetc(fd);

         if(feof(Nret))// Read to the end of the file and exit 
        {
    
            break;
        }
         fputc(Nret,stdout);// Output to the display  
     }
     flcose(fd);

      return 0;

}

 see   Source file  

 see   Other documents  

 Both files can be viewed    It proved successful