Installing gfortran in Cygwin

Question

I am trying to compile a modelling program in Cygwin using either a gfortran or g95 compiler. I have installed both compilers, but when I go to configure the program, it checks for the compilers and does not find then (error: Fortran compiler cannot create executables). I am new to Cygwin-- I suspect it is something with how/where I installed the compilers...Any ideas?

Thank you,

L.

Answer 1

For me, it's more helpful to have executable code to go through the process, so I'm going to put some in. This is addressing your concern,

I suspect it is something with how/where I installed the compilers...

because the installation from apt-cyg should be helpful in letting the system know where to look for the compilers. I'm also addressing a possible linkage issue.

bballdave025@MY-MACHINE /cygdrive/c/bballdave025
$ apt-cyg install gcc-fortran libgfortran5

If you don't have apt-cyg yet, follow these instructions from another answer.

# Get to where your setup executable lives.
# This is what you used to install Cygwin the first time.
# Note that mine is for the 64-bit version, and that
# I keep mine in C:\cygwin64. Your path might be
# different. You also might need to re-download
# The setup executable from Cygwin.

$ cd /path/to/setup_install/setup_x86-64.exe -q -P wget
$ wget https://raw.githubusercontent.com/transcode-open/apt-cyg/master/apt-cyg
$ chmod +x apt-cyg
$ mv apt-cyg /usr/local/bin

---

The libgfortran5 (or a more recent version, if available when you search) might be necessary. Here's why I think this might be the case.

bballdave025@MY-MACHINE /cygdrive/c/bballdave025
$ man gcc | grep -A 3 "[ ]*[-]l[ ]\{0,2\}library$"
       -llibrary
       -l library
           Search the library named library when linking.  (The second
           alternative with the library as a separate argument is only for
           POSIX compliance and is not recommended.)

(Note that I haven't included some parts of the result that aren't useful and can be fixed by prefixing the command with MANWIDTH=160, cf here.)

There is a little more detail and a little different result from the answer to a question about the lib prefix on files:

You can name a library whatever you want, but if you want gcc's -l flag to find the right one, you need to name it the way that link describes. For example, gcc -o myapp myapp.c -lm, [w]ill compile myapp.c, link the resulting object with libm.a, and output an executable called myapp. These days, there might be a more complicated search path involving dynamic library names, etc., but you should get the basic idea from this example. [In addition, you can look at this section f]rom the gcc man page:

-l library ...

... surrounds library with lib and .a and searches several directories.

The basic reason for all of that info is this: it is very possible that, in order to link with the gfortran library, you need to have installed a package named something like libgfortran. I don't know for sure how this works, especially with the Cygwin man page being slightly different, but it's worth a try. The likely extra thing you would need in this case is something like

apt-cyg install libgfortran

or

apt-cyg install libgfortran5

---

Here's some helpful info on how I found what to install. When I had a similar problem, I went to the Cygwin package search, but I only got three entries with three versions of netcdf-fortran

(archived). I wanted gfortran, so I kept looking

I found a great gfortran answer in this SO answer. With that answer, I went back to the Complete Cygwin Package List, armed with my trusty Ctrl + F, since I knew there were packages different from what came back from the search. The complete list had

cygwin64-gcc-fortran GCC for Cygwin 64bit toolchain (Fortran)`

gcc-fortran GNU Compiler Collection (Fortran)

and entries for libgfortran.

Hopefully some of this information will be helpful, or at least educational.

Answer 2

This problem is common for beginners with autotools. It can be:

1. missing libraries; this can be missing libraries for your project or compiler/system libraries, like libgfortran or similar for g95.
2. autotools can not detect your compiler;
3. dynamic libraries problem; runtime path to the dynamic libraries not set. See LD_LIBRARY_PATH for linux environment.
4. cross-compiling problem, I do not know much about cygwin but that can be an issue. I am not expert of cross-compiling either. It can also be another situation that I am not aware of.

I ran into the 1st and 3rd situations.

Approaches of solutions.

1. make sure you can manually compile and run a simple hello world program. Install the missing libraries if necessary. Also make sure that you can link your hello world program against the same libraries used by your modelling program, this last statement could lead you to the 3rd situation.
2. add the path to your compiler to the PATH variable or similar variable in cygwin. Or explicitly give the full path to your compiler to configure.
3. add the path to your libraries to the runtime libraries path LD_LIBRARY_PATH for linux environment or similar variable in cygwin. In one of my cases, the problem was that the test program that autotools uses to test the compiler could not run. It was successfully compiled but could not run. I installed all the libraries that my project uses in a path that was not included in library path. What happened was that the path to those libraries were set in the configure.ac or makefile.am so that the compiling was OK. But the running of the test program included in configure could not find them. This is a problem mostly for dynamically linked libraries. Adding the path to my .so to the LD_LIBRARY_PATH solved the problem.
4. well, I can not really help. The only solution that I can suggest is to install a linux system (dual boot or virtual machine) if you know how to do it, because I will not be there to help.

The following link can also help.