Ancient-Programming-Site/src/components/Fortran/Fortran_Set_Up.vue

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  <page-start>Setting Up The Environment</page-start>

  <paragraph>If you're familiar with C, then you would feel right at home with Fortran's build environment. There isn't really
    an "official" compiler for the language, only a standard, that has to be implemented by the compilers. But there
    are a lot of great compilers, that might as well be "official."<br><br>

    The top listed compiler on Fortran's website, is the GNU Fortran compiler (gfortran). It's the one I will be using
    throughout the examples on the site. Unless stated otherwise. There are also some other notable compilers, that
    has some rather interesting qualities to them.
  </paragraph>

  <p>Compilers:</p>
  <ul class="mb-6">
    <li>&gt; <a class="underline" href="https://lfortran.org/">lfortran</a> (This one can be used as an interactive
      compiler, supports parsing all of the 2018 standard syntax and also compile Fortran to WebAssemply).</li>
    <li>&gt; <a class="underline" href="https://developer.nvidia.com/hpc-sdk">NVIDIA HPC SDK</a> (This one comes with a whole lot of GPU
      accelerated libraries).</li>
  </ul>

  <paragraph>But we will be using gfortran. Through the examples on this site, I will mainly be focusing on developing on Linux. <br>
    First, we install the compiler.
  </paragraph>

  <p>For Fedora:</p>
  <code-tag>$ sudo dnf install gcc-gfortran</code-tag>

  <p>For ubuntu:</p>
  <code-tag>$ sudo apt install gfortran</code-tag>

  <paragraph>And that's it. Pretty easy.</paragraph>

  <h2 class="text-2xl">Project Structure</h2>
  <hr class="mb-6">

  <paragraph>When creating a Fortran project, or any project in general, you want a structure. There is a lot of different
    layouts for the structure, but equal amongst them, is the <code-tag>src</code-tag> folder. That's where we keep all of out
    source code. Like <code-tag>*.f90, *.f95</code-tag> files.<br><br>

    But other than that, most projects include a <code-tag>Makefile</code-tag> file, a
    <code-tag>library</code-tag>, <code-tag>test</code-tag>
    and <code-tag>bin</code-tag> folder. Your layout doesn't need to look like this specifically, nor does it have to contain
    the same folders. Each project is different, and so are the requirements. But this layout is simple, and great
    for medium to large projects.<br><br>

    But if we're doing micro-projects, as in like, a hello world application, a test application, or a small tool,
    this layout is rather redundant, and in the examples on this site, we will only use it on bigger projects,
    and we will let you know, when or how we set up the project.
  </paragraph>

  <div class="font-mono shadow-lg shadow-slate-500 p-2 mb-6">
<pre><code class="text-sm">
project/
├── src/          # Source files (.f90, .f95, etc.)
│   ├── modules/  # Module definitions
│   └── main.f90  # Main program file
├── include/      # Include files (interface definitions)
├── lib/          # Library object files and archives
├── bin/          # Executable binaries
├── tests/        # Test files
└── Makefile      # Build script
</code></pre>
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  <p>Notes:</p>
  <ul class="mb-6">
    <li>&gt; <code-tag>src</code-tag> (This is where we keep all of out source code).</li>
    <li>&gt; <code-tag>modules</code-tag> (This is where we keep our classes. Or in Fortran-speak, modules).</li>
    <li>&gt; <code-tag>include</code-tag> (This is where we keep our interfaces, that out modules will inherit from, if we're using Fortran 90 or above).</li>
    <li>&gt; <code-tag>bin</code-tag> (This is where the compiled program should end up in).</li>
  </ul>

  <h2 class="text-2xl">Compiling</h2>
  <hr class="mb-6">

  <paragraph>Makefiles are very useful, and becomes increasingly useful, the bigger the project gets. A makefile simplifies the
    compilation process, as all of the compile flags can be gathered inside a single file. It makes it possible to
    dynamically change the compilation depending on the system architecture or config. It also removes the need to
    manually compile and link your objects together, every time you make a change.<br><br>

    And with a bigger project, comes a big count of source files. That's where a makefile helps a lot, as it handles
    and tracks all changes to each file, ensuring that it's only the changed files that gets re-compiled.<br><br>

    So let's see a makefile in action. Below code is a simple Hello World application, that we will use a makefile to
    compile. Although it's worth noting, that a program this small, a makefile is wildly redundant. But it does show
    how it's set up in a simple environment.
  </paragraph>

  <code-tag>hello.f90</code-tag>
  <div class="font-mono shadow-lg shadow-slate-500 p-2 mb-6">
<pre><code class="text-sm">
program hello
    implicit none
    print *, 'Hello, World!'
end program hello
</code></pre>
    </div>

  <code-tag>Makefile</code-tag>
  <div class="font-mono shadow-lg shadow-slate-500 p-2 mb-6">
<pre><code class="text-sm">
FC = gfortran  # Fortran compiler
FFLAGS = -O2   # Compiler flags (optimization level)

hello: hello.o
    $(FC) $(FFLAGS) -o $@ $^

hello.o: hello.f90
    $(FC) $(FFLAGS) -c $<

run:
    ./hello

clean:
    rm -f *.o hello
</code></pre>
    </div>

  <paragraph>
    The makefile, in the eyes of a modern programmer (C#, Python, JS, Etc) might look rather repulsive. But be not
    afraid, because at the end of the day, it's simply just some rules, that the compiler follows to compile your program.
  </paragraph>

  <ul class="mb-6">
    <li>&gt; <code-tag>hello: hello.o</code-tag></li>
    <li class="pb-2">&gt; &gt; Here, the program "hello" depends on the object file "hello.o".</li>

    <li>&gt; <code-tag>$(FC) $(FFLAGS) -o $@ $^</code-tag></li>
    <li class="pb-2">&gt; &gt; This one compiles the object files into the program.</li>

    <li>&gt; <code-tag>hello.o: hello.f90</code-tag></li>
    <li class="pb-2">&gt; &gt; Here, the object file "hello.o" depends on the source file "hello.f90".</li>

    <li>&gt; <code-tag>$(FC) $(FFLAGS) -c $<</code-tag></li>
    <li class="pb-2">&gt; &gt; This one compiles the source files into the object files.</li>

    <li>&gt; <code-tag>run: ./hello</code-tag></li>
    <li class="pb-2">&gt; &gt; This runs the program if you execute <code-tag>make run</code-tag></li>

    <li>&gt; <code-tag>clean: rm -f *.o hello</code-tag></li>
    <li class="pb-2">&gt; &gt; Here, the object files gets removed when running <code-tag>make clean</code-tag></li>
  </ul>

  <paragraph>
    A quick note. It's very important that whenever something is indented in a makefile, that it's indented with a tab,
    and not 4 spaces. It needs to be a tab character.<br><br>

    Now simply run the makefile with the following command.
  </paragraph>

  <div class="font-mono shadow-lg shadow-slate-500 p-2 mb-6">
<pre><code class="text-sm">
$ make
gfortran   -O2    -c hello.f90
gfortran   -O2    -o hello hello.o
</code></pre>
  </div>

  <paragraph>
    We have now successfully compiled the program with the help of a makefile. Now simply run the program and we'll
    see the output.
  </paragraph>

  <div class="font-mono shadow-lg shadow-slate-500 p-2 mb-6">
<pre><code class="text-sm">
$ ./hello
 Hello, World!
</code></pre>
  </div>

  <paragraph>The exact same should happen, if we run the next command instead.</paragraph>

  <div class="font-mono shadow-lg shadow-slate-500 p-2 mb-6">
<pre><code class="text-sm">
$ make run
./hello
 Hello, World!
</code></pre>
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