Library Management System — C Implementation

A complete CRUD application for a library database, built in C using binary file I/O as the persistence layer. Includes both a console (terminal) interface and a GTK3 graphical interface.

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Database Model

Table	Key Fields
Authors	author_id, name, bio
Publishers	publisher_id, name, address, contact_info
Books	book_id, title, author_id(FK), publisher_id(FK), isbn, genre, year, copies, shelf
Members	member_id, name, address, phone, email, date_joined, membership_status
Staff	staff_id, name, role, email, phone
Borrowings	borrowing_id, book_id(FK), member_id(FK), borrow_date, due_date, return_date, staff_id(FK)
Fines	fine_id, borrowing_id(FK), amount, paid, date_paid

Data is stored as binary flat files in the data/ directory (one .dat file per table). Each file begins with a 4-byte next_id counter.

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Project Structure

library_system/
├── include/
│   ├── models.h        ← C structs for all 7 tables
│   ├── db.h            ← CRUD function declarations
│   ├── console_ui.h    ← Console menu declarations
│   └── gui_ui.h        ← GTK GUI declarations
├── src/
│   ├── db.c            ← File I/O CRUD (shared by both apps)
│   ├── console_ui.c    ← Interactive terminal menus
│   ├── gui_ui.c        ← GTK3 windowed interface
│   ├── main_console.c  ← Console entry point
│   └── main_gui.c      ← GUI entry point
├── data/               ← Auto-created at first run
└── Makefile

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Prerequisites

Console App

• GCC (any recent version)
• No external dependencies

GUI App

• GTK3 development libraries

Install GTK3:

# Ubuntu / Debian
sudo apt install libgtk-3-dev

# Fedora / RHEL
sudo dnf install gtk3-devel

# macOS (Homebrew)
brew install gtk+3

# Windows (MSYS2)
pacman -S mingw-w64-x86_64-gtk3

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Build & Run

cd library_system

# Build console app only
make console

# Build GUI app only (requires GTK3)
make gui

# Build both
make all

# Run console app
./library_console

# Run GUI app
./library_gui

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Console App — Usage

The console app presents a numbered menu system:

──────────────────────────────────────────────────
  LIBRARY MANAGEMENT SYSTEM  —  MAIN MENU
──────────────────────────────────────────────────
  1. Authors
  2. Publishers
  3. Books
  4. Members
  5. Staff
  6. Borrowings
  7. Fines
  0. Exit

Each sub-menu offers:

• Add a new record
• View / Search records
• Update an existing record
• Delete a record (soft-delete — data stays in file, marked inactive)

Special Borrowing features

• Return Book — automatically decrements copy count and calculates overdue fine (1.0 per day late)
• Overdue List — shows all unreturned borrowings past due date
• By Member — shows all borrowings for a specific member

Special Fine features

• Pay Fine — marks fine as paid, records today's date

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GUI App — Usage

The GTK3 GUI has a sidebar with one button per table. Click a table name to switch to its panel, which shows a live grid of records plus action buttons:

Button	Action
➕ Add	Opens a form dialog to insert a new record
✏️ Edit	Opens a pre-filled form to update the selected row
🗑 Delete	Confirms then soft-deletes the selected record
↩ Return Book	(Borrowings) processes a return + auto-fine
💳 Mark Paid	(Fines) marks a fine as paid

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Design Notes

File Layout

Each .dat file starts with a 4-byte integer (the next_id counter). Records are appended sequentially. Deletion sets the active flag to 0 (soft delete); queries skip inactive records.

The IMPL_CRUD Macro

db.c uses a C macro to generate all five CRUD functions for each table, keeping the codebase DRY. Only tables with extra operations (Borrowings, Fines) have additional hand-written functions.

FK Validation

The console and GUI both validate that referenced IDs exist before inserting a Borrowing. Copy counts are adjusted automatically.

Automatic Fine Calculation

When a book is returned late, borrowing_return_book() calculates (return_date − due_date) in days and inserts a Fine record automatically.

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Extending the Project

• Connect to real MySQL: replace db.c functions with mysql.h calls (the rest of the code stays identical).
• Add search: extend db.h / db.c with a *_search_by_name() function and hook it into the UI.
• Reports: add a Reports menu that aggregates borrowing stats, top books, overdue counts, etc.
• Authentication: add a login screen in the GUI before showing the main window.