gtkmm: Simple example fails to compile: gtkmm.h: No such file or directory - c++

Question

I am working through the gtkmm documentation. I have started by trying to compile the "Simple Example". Here is the code. It can also be found here.
/// SimpleExample.cpp
#include <gtkmm.h>
int main(int argc, char *argv[])
{
auto app =
Gtk::Application::create(argc, argv,
"org.gtkmm.examples.base");
Gtk::Window window;
window.set_default_size(200, 200);
return app->run(window);
}
I have tried to compile this using
g++ SimpleExample.cpp -o SimpleExample `pkg-config gtkmm-3.0 --cflags --libs`
which should work according to the documentation. (See end of linked page.)
Running pkg-config gtkmm-3.0 --cflags --libs produces
Package gtkmm-3.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gtkmm-3.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gtkmm-3.0' found
I am running Debian 9 Stretch. I installed gtkmm with
sudo apt update && sudo apt install libgtkmm-3.0-dev
Running find /usr -name "gtkmm" produces
/usr/lib/x86_64-linux-gnu/pkgconfig/gtkmm-3.0.pc
/usr/lib/x86_64-linux-gnu/gtkmm-3.0
/usr/lib/x86_64-linux-gnu/gtkmm-3.0/include/gtkmmconfig.h
/usr/include/gtkmm-3.0
/usr/include/gtkmm-3.0/gtkmm
/usr/include/gtkmm-3.0/gtkmm.h
So why does the example not compile?
Updates:
New terminal
pkg-config gtkmm-3.0 --cflags --libs
Package gtkmm-3.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gtkmm-3.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gtkmm-3.0' found
Try
find /usr -name "*gtkmm-3.0*"
/usr/lib/x86_64-linux-gnu/pkgconfig/gtkmm-3.0.pc
/usr/lib/x86_64-linux-gnu/libgtkmm-3.0.so.1.1.0
/usr/lib/x86_64-linux-gnu/libgtkmm-3.0.so.1
/usr/lib/x86_64-linux-gnu/gtkmm-3.0
/usr/lib/x86_64-linux-gnu/libgtkmm-3.0.so
/usr/share/doc/libgtkmm-3.0-1v5
/usr/share/doc/libgtkmm-3.0-dev
/usr/include/gtkmm-3.0
Export location
export PKG_CONFIG_PATH="/usr/lib/x86_64-linux-gnu/pkgconfig"
Re-run
pkg-config gtkmm-3.0 --cflags --libs
Package xproto was not found in the pkg-config search path.
Perhaps you should add the directory containing `xproto.pc'
to the PKG_CONFIG_PATH environment variable
Package 'xproto', required by 'xau', not found
(That's a different error this time.)
Try to find again
find /usr -name "*xproto*"
/usr/share/pkgconfig/xproto.pc
/usr/include/xcb/xproto.h
/usr/include/GL/glxproto.h
/usr/include/X11/extensions/lbxproto.h
Change export command
export PKG_CONFIG_PATH="/usr/lib/x86_64-linux-gnu/pkgconfig;/usr/share/pkgconfig"
Re-run, back to square 1
pkg-config gtkmm-3.0 --cflags --libs
Package gtkmm-3.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gtkmm-3.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gtkmm-3.0' found
Problem resolved (sort ot)
I have discovered from reading this question that the path should be colon seperated.
export PKG_CONFIG_PATH="/usr/lib/x86_64-linux-gnu/pkgconfig:/usr/share/pkgconfig"
However this does not solve the problem of why this variable needs to be set at all. pkg-config is used because it is supposed to make compilation simpler, however this isn't any more simple than specifying the include paths manually, as multiple environment variables need to be set.
In addition, the lack of information about this issue online makes me suspect that this is an issue which most users do not encounter, and therefore is probably specific to Debian 9. (I would like to know if anyone else has encounted this problem, and on what OS.)

Answer 1

At first, it is normal that installing gtkmm is a bit complicated. As far as i can see, here in the Stackoverflow forum many users have problem with doing so. Even users in the Windows operating system are confronted with error messages, if they are trying to use gtkmm together with Visual Studio for developing a platform independent app ... But to your question. There are many options what can go wrong. A simple explanation would be, that the debian package “libgtk-3-dev” has to be installed, which is used for creating GTK+ apps in C, because gtkmm uses this package. So the first step is to try out, it the compilation of a C sourcecode for GTK+ works. A second explanation is, that the debian “package manager” is in general broken so switching the Linux distribution would be a good advice. For example, in Fedora a simple dnf install gtk3 gtk3-devel gtkmm30 gtkmm30-devel is enough for starting programming.