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<div class="titlepage"><div><div><h1 class="title">
<a name="chapter-basics"></a>Chapter 3. Basics</h1></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<ul class="toc">
<li><span class="section"><a href="chapter-basics.html#sec-basics-simple-example">Simple Example</a></span></li>
<li><span class="section"><a href="sec-headers-and-linking.html">Headers and Linking</a></span></li>
<li><span class="section"><a href="sec-widgets-overview.html">Widgets</a></span></li>
<li><span class="section"><a href="sec-signals-overview.html">Signals</a></span></li>
<li><span class="section"><a href="sec-basics-ustring.html">Glib::ustring</a></span></li>
<li><span class="section"><a href="sec-basics-gobj-and-wrap.html">Mixing C and C++ APIs</a></span></li>
<li><span class="section"><a href="sec-helloworld.html">Hello World in <span class="application">gtkmm</span></a></span></li>
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<p>
This chapter will introduce some of the most important aspects of <span class="application">gtkmm</span> coding. These will be demonstrated with simple working example code. However, this is just a taster, so you need to look at the other chapters for more substantial information.
</p>
<p>
Your existing knowledge of C++ will help you with <span class="application">gtkmm</span> as it would with any library. Unless we state otherwise, you can expect <span class="application">gtkmm</span> classes to behave like any other C++ class, and you can expect to use your existing C++ techniques with <span class="application">gtkmm</span> classes.
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sec-basics-simple-example"></a>Simple Example</h2></div></div></div>
<p>
To begin our introduction to <span class="application">gtkmm</span>, we'll start with the simplest
program possible. This program will create an empty 200 x 200 pixel window.
</p>
<p><a class="ulink" href="https://gitlab.gnome.org/GNOME/gtkmm-documentation/tree/master/examples/book/base" target="_top">Source Code</a></p>
<p>File: <code class="filename">base.cc</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#include <gtkmm.h>
class MyWindow : public Gtk::Window
{
public:
MyWindow();
};
MyWindow::MyWindow()
{
set_title("Basic application");
set_default_size(200, 200);
}
int main(int argc, char* argv[])
{
auto app = Gtk::Application::create("org.gtkmm.examples.base");
return app->make_window_and_run<MyWindow>(argc, argv);
}
</code></pre>
<p>We will now explain each part of the example</p>
<pre class="programlisting"><code class="code">#include <gtkmm.h></code></pre>
<p>
All <span class="application">gtkmm</span> programs must include certain <span class="application">gtkmm</span> headers; <code class="literal">gtkmm.h</code>
includes the entire <span class="application">gtkmm</span> kit. This is usually not a good idea, because
it includes a megabyte or so of headers, but for simple programs, it
suffices.
</p>
<p>The next part of the program:</p>
<pre class="programlisting"><code class="code">class MyWindow : public Gtk::Window
{
public:
MyWindow();
};
MyWindow::MyWindow()
{
set_title("Basic application");
set_default_size(200, 200);
}</code></pre>
<p>
defines the <code class="classname">MyWindow</code> class. Its default constructor sets the
window's title and default (initial) size.
</p>
<p>The <code class="function">main()</code> function's first statement:</p>
<pre class="programlisting"><code class="code">auto app = Gtk::Application::create("org.gtkmm.examples.base");</code></pre>
<p>
creates a <code class="classname">Gtk::Application</code> object, stored in a <code class="classname">Glib::RefPtr</code> smartpointer.
This is needed in all <span class="application">gtkmm</span> applications. The <code class="methodname">create()</code> method for this object initializes <span class="application">gtkmm</span>.
</p>
<p>
The last line creates and shows a window and enters the <span class="application">gtkmm</span> main processing loop, which will finish when the window is closed.
Your <code class="function">main()</code> function will then return with an appropriate success or error code.
The <em class="parameter"><code>argc</code></em> and <em class="parameter"><code>argv</code></em> arguments, passed to your application on the command line,
can be checked when <code class="methodname">make_window_and_run()</code> is called, but this simple application does not use those arguments.
</p>
<pre class="programlisting"><code class="code">return app->make_window_and_run<MyWindow>(argc, argv);</code></pre>
<p>
After putting the source code in <code class="literal">simple.cc</code> you can compile
the above program with <span class="application">gcc</span> using:
</p>
<pre class="programlisting"><code class="code">g++ simple.cc -o simple `pkg-config --cflags --libs gtkmm-4.0` -std=c++17</code></pre>
<p>
Note that you must surround the <code class="literal">pkg-config</code> invocation with backquotes.
Backquotes cause the shell to execute the command inside them, and to use
the command's output as part of the command line.
Note also that <code class="literal">simple.cc</code> must come before the <code class="literal">pkg-config</code>
invocation on the command line. <code class="literal">-std=c++17</code> is necessary only if
your compiler is not C++17 compliant by default.
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