Question

Consider the following, partially-complete, C-program:
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>

#define BUFFERSIZE 100
#define COPYMODE 0644

main(int argC, char* argv[])
{
   int srcFd;
   int dstFd;
   int charCnt;
   char buf[BUFFERSIZE];
   /*Check args*/
   if( argC!=3 ){
       fprintf( stderr, "usage: %s source destination\n", argv[0]);
       exit(1);
   }
   /*Open the files*/
  
   srcFd= open(argv[1],O_RDONLY);
   if( srcFd==-1 ){
       fprintf(stderr,"Cannot open %s \n", argv[1]);
   }

   dstFd= creat(argv[2],COPYMODE);

   if( dstFd==-1 ){
       fprintf( stderr,"Cannot create %s \n", argv[2]);
   }
   /* put your code to copy from srcFd to dstFd here */
   /* code to close files would go here. */
}
This program opens up a source file to be accessed with: srcFd and a
destination file to be accessed with: dstFd. There is code missing to
copy the contents of srcFd to dstFd.
Write C to to replace the comment:
/* put your code to copy from srcFd to dstFd here */
which copies the content of the source file to the destination file. Your
code should check for reading and writing errors as it goes and print
the appropriate messages to stderr. Note, you do not need to write
code to close the files.

Answer 1

Below is the code of the above problem.

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include<unistd.h>
#define BUFFERSIZE 100
#define COPYMODE 0644

int main(int argC, char* argv[])
{
   int srcFd;    //source file descriptor
   int dstFd;    //destination file descriptor
   int charCnt;   //variable to count no of character of transfer
   char buf[BUFFERSIZE]; //buffer to temporary store transfering data
   /*Check args*/
   if( argC!=3 ){
       fprintf( stderr, "usage: %s source destination\n", argv[0]);
       exit(1);
   }
   /*Open the files*/

   srcFd= open(argv[1],O_RDONLY);
   if( srcFd==-1 ){
       fprintf(stderr,"Cannot open %s \n", argv[1]);
   }

   dstFd= creat(argv[2],COPYMODE);

   if( dstFd==-1 ){
       fprintf( stderr,"Cannot create %s \n", argv[2]);
   }

/*code to copy from source file to destination file*/
//read system call take three arguments i.e source file descriptor,buffer, max size of data to read
//read return size of read data
//write is also same as read except that instead of source file descriptor, destination file descriptor is used.
   while((charCnt=read(srcFd,buf,BUFFERSIZE)) > 0)
       {
  
           if(write(dstFd,buf,charCnt) != charCnt)
               {
               perror("unable to write\n");
               exit(1);                  
           }
       }
/*code to close files*/
//close system call is used to close the file descriptor
//close takes file descriptor to be closed as argument
//on success close, return +ve integer
   if(close(srcFd)<0)
       {
           perror("unable to close source file descriptor\n");
           exit(1);
       }
   if(close(dstFd)<0)
       {
           perror("unable to close source file descriptor\n");
           exit(1);
       }

}

OUTPUT:

karan@karan-Inspiron-15-3567:~$ ./a.out file1.txt file2.txt

karan@karan-Inspiron-15-3567:~$ cat file1.txt

this is the text file to check
whether program is working fine or not
thank you

karan@karan-Inspiron-15-3567:~$ cat file2.txt
this is the text file to check
whether program is working fine or not
thank you