Question

Rewrite the attached code program using read, write, open and close (System I/O functions) instead of the standard I/O functions. Also please write comments explaining each line of code clearly and concisely please.

#include
#include

int main(int argc, char *argv[])
{ FILE *fd;
   char c;

   if(argc==1)
   fd=stdin;
   else
        if((fd = fopen(argv[1], "r"))==NULL){
       fprintf(stderr, "Error opening %s, exiting\n", argv[1]);            exit(0);
   }

   while( (c=getc(fd)) != EOF)
   putc(c, stdout);

   exit(0);
}

Answer 1

SOLUTION

#include<stdio.h>
#include<fcntl.h>
//we need to import fcntl to give the modes of opening the files like O_RDONLY
#include<stdlib.h>
#include<string.h>
//string.h to have the string methods
int main(int argc, char *argv[])
{
int fd;
//here in system calls we will defimee the file descriptor fd unilike the File pointer in the
// here fd has three paramets 0- input,1- output 2- standard error
char c;
if(argc==2)
{
   //open the first file in the read, write mode and check if file is opened successfully or not if not exit from the program
       fd = open(argv[1], O_RDWR);
       //it is unable to open the file it will return -1
       if((fd)==-1){
           //Failed to open it will return the fd as -1
        printf("\nError opening the file") ;
        exit(1);
        }
        while(read(fd,&c,1)!=0){
            //priint data read will return the number of items read (read takes 3 parameters 1->filedescriptor,2-> buffer to store data, 3->number of items to be read)
            printf("%c",c);
       }
       //write data to the file(write takes 3 paramets same as read )
        write(fd,"Hello",strlen("HelloS"));
       while(read(fd,&c,1)!=0){
            printf("%c",c);
       }
   }
   //close the file
close(fd);
}

OUTPUT

This is the output after running the program two times so it has two hello inserts

FIle: