I am coming from KDE to XFCE and hence arrive from KDevelop at Geany. I have no plans of using Geany for any compilation stuff, prefering to write my own CMakeLists.txt files. However, what I loved about KDevelop and dearly would have again:
In KDevelop I could "attach" an include-directory to a c++ file meaning that code autocompletion would look for #included headers within that directory and use its content.
For example it was possible to "attach" something like /usr/share/myIncludes/ containing "my_foo.h". Then in the source code of my program I would
#include "my_foo.h"
and henceforth auto-completion would kick in using the contents of "my_foo.h".
I find this surprisingly hard to google. Is there even a feature like that in Geany, and if so, how would one use it?
My Geany is a simple install (geany and geany-common) on a clean (no non-free stuff) Debian System.
Geany is not supporting dynamic parsing of header files due to the performances and resources impact it would have.
However, you can generate a tag file from your headers as described inside manual or maybe use a plugin like geanyctags or projectorganizer (recently rename from gproject) which could help you there
Also you can find tag-files inside the wiki which you can import via the Tools-menu.