I’ve just installed Haiku r1beta5-x86_64 as a QEMU/KVM virtual machine and started playing around, and then observed a weird gfortran compilation warning:
Hello @KazuFurutaka, and welcome! It’s always a pleasure to see another Fortraner in Haiku.
I get the same warning, which is still there even if I inhibit all warning messages (gfortran -w ...). So if even that won’t suppress the warning message, I don’t know what else will. Clearly a bug, which I didn’t report since @BiPolar already did.
Despite that, however, gfortran works very well in Haiku. I use it extensively without issues, even with bindings to C low-level libraries (such as OpenGL, OpenAL, etc). Makefiles are basically the same as in any *nix-like system; in large projects, with custom libraries used, you might want to set the system’s default include and lib directories (with the -I flag while compiling and -L while linking). Other than that, there is no difference when working with gfortran (and GCC in general) in Haiku.
I often forget what operating system I am using, since all the tools needed are there anyway. So don’t let that little warning fool you.