Computer Science – File handling | e-Consult

A program accesses data stored in an external file through a series of steps involving the operating system (OS). Here's a breakdown:

1. File Path Specification: The program specifies the location of the file using a file path. This path can be either:

   • Absolute Path: A complete path that specifies the exact location of the file, starting from the root directory (e.g., C:\Users\Username\Documents\data.txt on Windows, or /home/username/documents/data.txt on Linux/macOS).
   • Relative Path: A path specified relative to the program's current working directory (e.g., data.txt if the file is in the same directory as the program, or data/info.txt if the file is in a subdirectory named "info").

2. Operating System Interaction: The program uses system calls (provided by the OS) to request access to the file. These calls include specifying the file path and the desired access mode (read, write, etc.).
3. File System Management: The OS's file system manages the storage and retrieval of files on the storage device. It translates the file path into a physical location on the disk.
4. File Opening: The OS opens the file, allocating resources (memory buffers, etc.) to allow the program to access the data.
5. Data Retrieval/Modification: The program then reads from or writes to the file using the specified access mode.
6. File Closing: Finally, the program closes the file, releasing the allocated resources. This is important to ensure data integrity and prevent resource leaks.

The OS plays a vital role in security and permissions. It checks if the program has the necessary permissions to access the file based on user accounts and file system settings. Without the correct permissions, the program will be denied access.