Adde README files for each chapter folder

chp4/README.md

@@ -0,0 +1,42 @@
+# Chapter 3 – Advanced File I/O
+
+## File Metadata and the `stat` Family
+- Use `stat()`, `fstat()`, `lstat()` to retrieve file metadata:
+  - File type, size, inode number, permissions, ownership, timestamps (atime, mtime, ctime).
+- The `stat` structure includes all these details.
+
+## File Types
+- Regular file, directory, symbolic link, character/block device, FIFO, socket.
+- Use macros like `S_ISREG()`, `S_ISDIR()` to test file types.
+
+## File Permissions and Modes
+- Represented by 12 bits (e.g., `rwxr-xr--`), plus sticky/SUID/SGID bits.
+- Manipulate with `chmod()`, `fchmod()`, `umask()`.
+- Ownership changed with `chown()` and `fchown()`.
+
+## Links
+- **Hard links**: multiple filenames point to the same inode.
+- **Symbolic links**: separate files that reference other paths; can be broken.
+- Use `link()`, `unlink()`, `symlink()`, `readlink()`.
+
+## Directories
+- Open with `opendir()`, read entries with `readdir()`.
+- Low-level: `getdents()` system call.
+
+## File Timestamps
+- `utime()`, `utimes()`, `futimens()`, and `utimensat()` to update access/modification times.
+
+## File Descriptors and Flags
+- Manipulate with `fcntl()`:
+  - Set non-blocking mode (`O_NONBLOCK`), FD_CLOEXEC flag, file locks.
+  - Duplicate with `dup()` and `dup2()`.
+
+## File Locking
+- `flock()` for advisory locking (whole file).
+- `fcntl()` for POSIX record locking (ranges).
+
+## Temporary Files
+- `tmpfile()`, `mkstemp()` are safe methods to create temp files.
+
+## Summary
+- Chapter 3 focuses on extended file handling: metadata, links, directories, file modes, and advanced descriptor manipulation.