On 26 Apr 2021, at 18:38, ken williams wrote:
>
> This is from my everyday machine, which has FLTK 1.4 build in home path, but it's not installed.
> Thanks!
>
> [ken01@Manjaro home]$ which fltk-config
> /usr/local/bin/fltk-config

OK - so this tells us that your shell (and therefore, by extension, your Makefile) are finding and using a fltk-config located in "/usr/local/bin”, which is not the fltk-config in your home folder path (which you have not installed.)

So this would seem to imply there is more than one fltk-1.4 present on your system, I guess, since the next line shows us that the fltk-config your shell finds reports itself to be 1.4.0.

> [ken01@Manjaro home]$ fltk-config --version
> 1.4.0


>
> [ken01@Manjaro home]$ fltk-config --cxxflags
> -I/usr/local/include -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -D_THREAD_SAFE -D_REENTRANT
>
> [ken01@Manjaro home]$ fltk-config --ldflags
> -L/usr/local/lib -lfltk -lm -lX11 -lXext -lpthread -lXinerama -lXfixes -lXcursor -lXft -lXrender -lm -lfontconfig -ldl
>
> [ken01@Manjaro home]$ fltk-config --includedir
> /usr/local/include


That all looks reasonable, but shows us that the fltk-config your Makefile is calling will be using include files from "/usr/local/include" and libraries linked from "/usr/local/lib" so, again, not the version in your “home" folders.

These are fairly normal install locations on most Linux distros.
Do you know what fltk is actually installed in these locations?
Indeed, is *any* fltk actually installed there at all, or is the fltk-config lying to us?

If you go to "/usr/local/include/FL" is there in fact a folder there, and does it have the various FL header files in it?
Does the file "/usr/local/lib/libfltk.a" exist? Along with the other fltk libs (libfltk_forms.a, libfltk_gl.a, libfltk_images.a)?