Question

int main(int argc, char *argv[]){ 
 int fd1, fd2;
 char buffer[100];  long int n1;

 if(((fd1 = open(argv[1], O_RDONLY)) == -1) ||  ((fd2 = open(argv[2],  
       O_CREAT|O_WRONLY|O_TRUNC,0700)) == -1)){
     perror("file problem ");  
     exit(1);
 }

 while((n1=read(fd1, buffer, 512) > 0))  
      if(write(fd2, buffer, n1) != n1){
             perror("writing problem ");  exit(3);
       }

// Case of an error exit from the loop  
 if(n1 == -1){
    perror("Reading problem ");  
    exit(2);
  }
  close(fd2);  
  exit(0);
}

Could anyone fix the two issues in the while loop, so the ouput can be "writing problem : Bad file descriptor"

Answer 1

We need to just read byte by byte from the file i.e. instead of 512 bytes we need to read 1 byte at a time. I just changed the line

while((n1=read(fd1, buffer, 512) > 0))
to
while((n1=read(fd1, buffer, 1) > 0))
now my contents in 1st file are getiing copied and written to 2nd file.

I'm attaching my code below:

#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>

int main(int argc, char *argv[]){
int fd1, fd2;
char buffer[100]; long int n1;
fd1= open(argv[1], O_RDONLY);
fd2 = open(argv[2],O_CREAT|O_WRONLY|O_TRUNC,0700);

if(fd1==-1 || fd2 == -1){
perror("file problem ");
exit(1);
}

//char buffer[20];
size_t nbytes;
ssize_t bytes_read;

while((n1=read(fd1, buffer, 1) > 0))
if(write(fd2, buffer, n1) != n1){
perror("writing problem "); exit(3);
}

// Case of an error exit from the loop
if(n1 == -1){
perror("Reading problem ");
exit(2);
}
close(fd2);
exit(0);
}