Question

Assignment: Lab Experiment If you open a file for read-write with the append flag, can you still read from anywhere in the file using Iseek? Can you use Iseek to set the offset and call write to replace existing data in the file? Write a program to verify this. s0

Answer 1

The answer is No.

When we try to open a file for read-write with append flag all the data will be wriiten to the end.

Basically what ever the position of file pointer the data written will only append.

The file opening with append can be done with O_APPEND Flag

Below is the sample code snippet

Here I am taking sample.txt for file operation . Ensure it is present in your current directory .

Content of sample.txt

This is line 1
This is line 2
This is line 3
This is line 4
This is line 5
This is line 6
This is line 7
This is line 8
This is line 9
This is line 10

Below is the code:

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

int main() {
int fd = open("sample.txt", O_WRONLY | O_APPEND);

lseek(fd, 0, SEEK_SET);
write(fd, "abc", 3);
close(fd);
  
return 0;
}

File content of sample.txt after program execution:

This is line 1
This is line 2
This is line 3
This is line 4
This is line 5
This is line 6
This is line 7
This is line 8
This is line 9
This is line 10