added hello world in gtkmm (C++)

Author: senarclens

hello/.gitignore

@@ -0,0 +1 @@
+hello

hello/README.md

@@ -0,0 +1 @@
+g++ main.cpp hello.cpp -o hello `pkg-config --cflags --libs gtkmm-4.0` -std=c++20

hello/hello.cpp

@@ -0,0 +1,22 @@
+#include "hello.hpp"
+
+#include <iostream>
+
+Hello::Hello() : button_("Hello World") {
+  button_.set_margin(10);
+
+  button_.signal_clicked().connect(sigc::mem_fun(*this,
+              &Hello::on_button_clicked));
+
+  // This packs the button into the Window (a container).
+  set_child(button_);
+}
+
+Hello::~Hello() {
+}
+
+void Hello::on_button_clicked()
+{
+  std::cout << "Hello World" << std::endl;
+}
+

hello/hello.hpp

@@ -0,0 +1,20 @@
+#ifndef HELLO_HPP
+#define HELLO_HPP
+
+#include <gtkmm/button.h>
+#include <gtkmm/window.h>
+
+class Hello : public Gtk::Window {
+public:
+  Hello();
+  ~Hello() override;
+
+protected:
+  //Signal handlers:
+  void on_button_clicked();
+
+  //Member widgets:
+  Gtk::Button button_;
+};
+
+#endif  // HELLO_HPP

hello/main.cpp

@@ -0,0 +1,10 @@
+#include "hello.hpp"
+
+#include <gtkmm/application.h>
+
+int main(int argc, char* argv[]) {
+  auto app = Gtk::Application::create("org.gtkmm.example");
+
+  //Shows the window and returns when it is closed.
+  return app->make_window_and_run<Hello>(argc, argv);
+}