## Getting Started with GTK+

This chapter contains some tutorial information to get you started with GTK+ programming. It assumes that you have GTK+, its dependencies and a C compiler installed and ready to use. If you need to build GTK+ itself first, refer to the Compiling the GTK+ libraries section in this reference.

## Basics

To begin our introduction to GTK, we'll start with the simplest program possible. This program will create an empty 200 × 200 pixel window.

Create a new file with the following content named example-0.c.

    FIXME: MISSING XINCLUDE CONTENT

You can compile the program above with GCC using:

`gcc `pkg-config --cflags gtk+-3.0` -o example-0 example-0.c `pkg-config --libs gtk+-3.0``

For more information on how to compile a GTK+ application, please refer to the Compiling GTK+ Applications section in this reference.

All GTK+ applications will, of course, include `gtk/gtk.h`, which declares functions, types and macros required by GTK+ applications.

Even if GTK+ installs multiple header files, only the top-level `gtk/gtk.h` header can be directly included by third party code. The compiler will abort with an error if any other header is directly included.

We then proceed into the `main`() function of the application, and we declare a `window` variable as a pointer of type GtkWidget.

The following line will call `gtk_init()`, which is the initialization function for GTK+; this function will set up GTK+, the type system, the connection to the windowing environment, etc. The `gtk_init()` takes as arguments the pointers to the command line arguments counter and string array; this allows GTK+ to parse specific command line arguments that control the behavior of GTK+ itself. The parsed arguments will be removed from the array, leaving the unrecognized ones for your application to parse.

For more information on which command line arguments GTK+ recognizes, please refer to the Running GTK+ Applications section in this reference.

The call to `gtk_window_new()` will create a new GtkWindow and store it inside the `window` variable. The type of the window is `GTK_WINDOW_TOPLEVEL`, which means that the GtkWindow will be managed by the windowing system: it will have a frame, a title bar and window controls, depending on the platform.

In order to terminate the application when the GtkWindow is destroyed, we connect the “destroy” signal to the `gtk_main_quit()` function. This function will terminate the GTK+ main loop started by calling `gtk_main()` later. The “destroy” signal is emitted when a widget is destroyed, either by explicitly calling `gtk_widget_destroy()` or when the widget is unparented. Top-level GtkWindows are also destroyed when the Close window control button is clicked.

GtkWidgets are hidden by default. By calling `gtk_widget_show()` on a GtkWidget we are asking GTK+ to set the visibility attribute so that it can be displayed. All this work is done after the main loop has been started.

The last line of interest is the call to `gtk_main()`. This function will start the GTK+ main loop and will block the control flow of the `main()` until the `gtk_main_quit()` function is called.

While the program is running, GTK+ is receiving events. These are typically input events caused by the user interacting with your program, but also things like messages from the window manager or other applications. GTK+ processes these and as a result, signals may be emitted on your widgets. Connecting handlers for these signals is how you normally make your program do something in response to user input.

The following example is slightly more complex, and tries to showcase some of the capabilities of GTK+.

In the long tradition of programming languages and libraries, it is called Hello, World.

Example 1. Hello World in GTK+

Create a new file with the following content named example-1.c.

    FIXME: MISSING XINCLUDE CONTENT

You can compile the program above with GCC using:

`gcc `pkg-config --cflags gtk+-3.0` -o example-1 example-1.c `pkg-config --libs gtk+-3.0``