GUI Programming with C Language on Linux Platform

When you say you gonna write a GUI application in C for Linux platform, some people may laugh at you saying it is really really hard to write GUI applications in C and you will have to write thousands of lines of codes to get even simple GUI components working. However it is not true. You can write very nice GUI applications with C and you don't have to put that much big effort for it.
   
There are different libraries available for writing GUI applications in Linux. Among all these, GTK+ is an interesting library which I have been explored recently. GTK stands for GIMP Tool Kit and it was originally developed for GIMP(GNU Image Manipulation Program). Currently GTK+ has been used for so many applications and specially it has been used for developing GNOME desktop environment.

Before developing applications with GTK+, you have to install it. You can install it by typing the following on the terminal.

sudo apt-get install build-essential
sudo apt-get install libgtk2.0-doc devhelp

Now it's time write some codes and explore. Open your favourite text editor and add the following code into it. Save this file as "first.c".

1:  #include <gtk/gtk.h>  
2:  int main( int  argc,  
3:       char *argv[] )  
4:  {  
5:    GtkWidget *window;  
6:    gtk_init (&argc, &argv);  
7:    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);  
8:    gtk_widget_show (window);  
9:    gtk_main ();  
10:    return 0;  
11:  }  

You can compile this program in the terminal by issuing the following command. You should note that the single quote used here is this (`) one, not this (') one.

gcc first.c -o first `pkg-config --cflags --libs gtk+-2.0`

Run the executable program by typing ./first on the terminal. You will see a window like the one showed in the Figure:1. But when you close the window you will notice that the program doesn't exit from the terminal even the window disappears. You have to put a CTRL+C to exit. This is because our simple program doesn't handle events such as mouse click in different places.

Figure-1

Lets explore much improved program. Copy the following code to a new file and save it as "second.c".

1:  #include<gtk/gtk.h>  
2:  void hello(GtkWidget* widget, gpointer data){  
3:       g_print("Hello World\n");  
4:  }  
5:  gint delete_event_handler(GtkWidget* widget, GdkEvent* event, gpointer data){  
6:       g_print("delete event occured\n");  
7:       return FALSE;  
8:  }  
9:  void destroy(GtkWidget* widget, gpointer data){  
10:       gtk_main_quit();  
11:  }  
12:  int main(int argc, char *argv[]){  
13:       GtkWidget *window;  
14:       GtkWidget *button;  
15:       gtk_init(&argc, &argv);  
16:       window = gtk_window_new(GTK_WINDOW_TOPLEVEL);  
17:       g_signal_connect(G_OBJECT(window), "delete_event", G_CALLBACK(delete_event_handler), NULL);  
18:       g_signal_connect(G_OBJECT(window), "destroy", G_CALLBACK(destroy), NULL);  
19:       gtk_container_set_border_width(GTK_CONTAINER(window), 10);  
20:       button = gtk_button_new_with_label("Hello World");  
21:       g_signal_connect(G_OBJECT(button), "clicked", G_CALLBACK(hello), NULL);  
22:       gtk_container_add(GTK_CONTAINER(window), button);  
23:       gtk_widget_show(button);  
24:       gtk_widget_show(window);  
25:       gtk_main();  
26:       return 0;  
27:  }  

Compile and run this program by issuing following commands in the terminal.

gcc second.c -o second `pkg-config --cflags --libs gtk+-2.0`
./second

This time you have a window with a button. Click on the "Hello World" button and seen how the mouse click event is handled by the hello() function that we have declared and it prints "Hello World" string in the terminal. Click the close button for issuing a delete event and see how the program get exited by calling gtk_main_quit() function inside the destroy() event handler function.

Figure-2

 

Having a good understanding about how to register event handlers with the widgets and how to pack the widgets inside the window is necessary for learning to use GTK+. There's a good GTK+ tutorial here that can be viewed online or even off-line by downloading. Different example codes are also included in it and is very helpful. Go though it and explore what are the things you can do with GTK+.

Enjoy GUI programming in C!