GTKmm header files seem to be missing when I try to compile my program

Question

I am trying to compile a GTKmm C++ program using g++ (clang), however I can't seem to find the header files that I need. I have run the installation .sh file for GTK+, and I have also tried directly installing GTKmm via Homebrew, but I am still getting this error:

fatal error: 'gtkmm/button.h' file not found

I thought it would be as simple as adding an include directory, but I have tried searching my hard drive for GTK-related things and am still not finding anything. What should I do?

I am using a Macbook running MacOS Big Sur.

Update: My code is this:

helloworld.h

#ifndef GTKMM_EXAMPLE_HELLOWORLD_H
#define GTKMM_EXAMPLE_HELLOWORLD_H

#include <gtkmm/button.h>
#include <gtkmm/window.h>

class HelloWorld : public Gtk::Window {
    public:
        HelloWorld();
        virtual ~HelloWorld();

    protected:
        //Signal handlers:
        void on_button_clicked();

        //Member widgets:
        Gtk::Button m_button;
};

#endif

helloworld.cpp

#include "helloworld.h"
#include <iostream>

HelloWorld::HelloWorld()
: m_button("Hello World")   // creates a new button with label "Hello World".
{
    // Sets the border width of the window.
    set_border_width(10);

    // When the button receives the "clicked" signal, it will call the
    // on_button_clicked() method defined below.
    m_button.signal_clicked().connect(sigc::mem_fun(*this,
              &HelloWorld::on_button_clicked));

    // This packs the button into the Window (a container).
    add(m_button);

    // The final step is to display this newly created widget...
    m_button.show();
}

HelloWorld::~HelloWorld()
{
}

void HelloWorld::on_button_clicked()
{
    std::cout << "Hello World" << std::endl;
}

main.cpp

#include "helloworld.h"
#include <gtkmm/application.h>

int main (int argc, char *argv[]) {
    auto app = Gtk::Application::create(argc, argv, "org.gtkmm.example");

    HelloWorld helloworld;

    //Shows the window and returns when it is closed.
    return app->run(helloworld);
}

This code comes from here.

I am compiling by first navigating to the directory of the files listed above, and running g++ main.cpp -o helloworld.

Because I have installed Homebrew, g++ uses clang++.

Answer 1

Ok, I have figured it out.

I needed to install both GTK+ and GTKmm via Homebrew. This put the library into /usr/local/include. Note that the question code still won't work, because it is using the wrong directory (I installed gtk+3 and gtkmm3). Refer to this answer for more information.