GTK (GIMP Toolkit) is a powerful, open-source toolkit for creating graphical user interfaces (GUIs). It is built on top of GLib and used by applications like GIMP, Inkscape or Gnumeric.

GTK uses an object-oriented programming model in C through a system called GObject, and it integrates tightly with GLib for event loops, signals, and utilities.

First GTK Program: A Simple Window

#include <gtk/gtk.h>

int main(int argc, char *argv[]) {
    gtk_init(&argc, &argv);

    GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "Hello, GTK!");
    gtk_window_set_default_size(GTK_WINDOW(window), 300, 200);

    g_signal_connect(window, "destroy", G_CALLBACK(gtk_main_quit), NULL);

    gtk_widget_show_all(window);
    gtk_main();

    return 0;
}

Step-by-Step Breakdown

1. #include <gtk/gtk.h>

This includes the complete GTK+ header.

• Provides access to widgets like GtkWindow, GtkButton, GtkLabel, and layout containers.
• Also includes GLib and GObject headers automatically.

• 2. gtk_init(&argc, &argv);

Initializes GTK and parses any GTK-specific command-line options.

• You must call this before using any GTK functions.
• It modifies argc/argv to remove GTK-related flags.

3. Creating a Window

GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);

• Creates a new top-level application window.
• GtkWidget is a generic pointer for all GTK widgets.

4. Setting Window Properties

gtk_window_set_title(GTK_WINDOW(window), "Hello, GTK!");
gtk_window_set_default_size(GTK_WINDOW(window), 300, 200);

• Sets the window title and default size (in pixels).
• GTK_WINDOW() is a macro that casts to GtkWindow* safely.

• 5. Handling Events (Signals)

g_signal_connect(window, "destroy", G_CALLBACK(gtk_main_quit), NULL);

• GTK uses a signal system to handle events.
• "destroy" is emitted when the window is closed.
• gtk_main_quit stops the GTK event loop, ending the application.

6. Displaying Widgets

gtk_widget_show_all(window);

• Makes the window (and any contained widgets) visible.

7. Entering the Main Loop

gtk_main();

• Starts the GTK event loop, which waits for and dispatches events (keyboard, mouse, etc.).
• Your program stays here until gtk_main_quit() is called.

Compilation with GTK

Use pkg-config with GTK for proper flags and linking:

gcc gtk_example.c $(pkg-config --cflags --libs gtk4) -o gtk_example

If you’re using GTK 3 instead of GTK 4, replace gtk4 with gtk+-3.0:

gcc gtk_example.c $(pkg-config --cflags --libs gtk+-3.0) -o gtk_example

Output

Running the program will show a basic empty window titled “Hello, GTK!”.

GTK and GLib

GTK depends on both GLib and GObject, so understanding them is helpful for larger applications.

More information

You can refer to https://docs.gtk.org/ to see more information about using Glib and GTK

Summary

GTK allows you to build native desktop applications in C with windows, buttons, and layouts. It builds on top of GLib and GObject, giving you a full-featured and portable GUI toolkit using C.