Thread: writing to a file after using lseek

If I set lseek to say an offset of 20000 after the END of file, why can't I write the string "hello" at this position??

Code:

/*if you read data after end of file, buffer displays NULL*/

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

#define BUFFERSIZE 4096

int main(int ac, char *argv[])
{
	int fd1;
	ssize_t nread,nwrite,nbytes ;
	off_t newpos;
	char buf[BUFFERSIZE];
	
	fd1 = open("b.txt", O_RDWR);
		
	if (fd1 == -1)
		perror("error");
	
	//offset 20000 positions after end of file
	newpos = lseek(fd1, 20000, SEEK_END);

	nread = (fd1,buf,20);
	
	printf("buffer contains: %s\n", buf);

	strcpy(buf, "hello");
	nbytes = strlen(buf);
	printf("buffer contains: %s\n", buf);
	
	nwrite = (fd1,buf,20);

	if (nwrite == -1)
		perror("error here");


	

}

Originally Posted by GReaper

Putting everything else aside, what do you think lines #24 and #32 are doing?

thanks for reply. This is what I think L24 and L32 does

line 24 --> take 20 haracters from file identified by fd and place them in buffer.

I'm assuming this takes 20 charcters at the "20000th position"

line 32 --> Write to file from buffer 20 characters at a time
I'm assuming it will write hello and a few NULL characters