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

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    <h1 class="text-3xl">Setting Up The Environment</h1>
    <hr class="mb-6">

    <p class="mb-6">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.</p>

    <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>

    <p class="mb-6">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.</p>

    <p>For Fedora.</p>
    <code class="text-red-500 mb-6">$ sudo dnf install gcc-gfortran</code>

    <p>For ubuntu.</p>
    <code class="text-red-500 mb-6">$ sudo apt install gfortran</code>

    <p class="mb-6">And that's it. Pretty easy.</p>

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

    <p class="mb-6">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 class="text-red-500">src</code> folder. That's where we keep all of out
      source code. Like <code class="text-red-500">*.f90, *.f95</code> files.<br><br>

      But other than that, most projects include a <code class="text-red-500">Makefile</code> file, a
      <code class="text-red-500">library</code>, <code class="text-red-500">test</code>
      and <code class="text-red-500">bin</code> 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.</p>

    <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 (e.g., interface definitions)
├── lib/          # Library object files and archives
├── bin/          # Executable binaries
├── tests/        # Test cases
└── Makefile      # Build script
</code></pre>
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    <br>

    <p>Notes:</p>
    <ul class="mb-6">
      <li>&gt; <code class="text-red-500">src</code> (This is where we keep all of out source code).</li>
      <li>&gt; <code class="text-red-500">modules</code> (This is where we keep our classes. Or in Fortran-speak, modules).</li>
      <li>&gt; <code class="text-red-500">include</code> (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 class="text-red-500">bin</code> (This is where the compiled program should end up in).</li>
    </ul>


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

    <p class="mb-6">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.</p>


    <code class="text-red-500">hello.f90</code>
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<pre><code class="text-sm">
program hello
    implicit none
    print *, 'Hello, World!'
end program hello
</code></pre>
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    <p class="mb-6">The makefile, in the eyes of a modern programmer (C#, Python, JS, Etc) might look rather repulsive. But be not
      afraid. It will all make sense in a bit.</p>

    <ul>
      <li>&gt; <code class="text-red-500">hello: hello.o</code></li>
      <li class="pb-2">&gt; &gt; Here, the program "hello" depends on the object file "hello.o".</li>
      <li>&gt; <code class="text-red-500">$(FC) $(FFLAGS) -o $@ $^</code></li>
      <li class="pb-2">&gt; &gt; This one compiles the object files into the program.</li>
      <li>&gt; <code class="text-red-500">hello.o: hello.f90</code></li>
      <li class="pb-2">&gt; &gt; Here, the object file "hello.o" depends on the source file "hello.f90".</li>
      <li>&gt; <code class="text-red-500">$(FC) $(FFLAGS) -c $<</code></li>
      <li class="pb-2">&gt; &gt; This one compiles the source files into the object files.</li>
      <li>&gt; <code class="text-red-500">run: ./hello</code></li>
      <li class="pb-2">&gt; &gt; This runs the program if you execute <code class="text-red-500">make run</code></li>
      <li>&gt; <code class="text-red-500">clean: rm -f *.o hello</code></li>
      <li class="pb-2">&gt; &gt; Here, the object files gets removed when running <code class="text-red-500">make clean</code></li>
    </ul>
    <br>

    <p class="mb-6">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.</p>

    <code class="text-red-500">makefile</code>
    <div class="font-mono shadow-lg shadow-slate-500 p-2 mb-6">
<pre><code class="text-sm">
Makefile for hello.f90

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>
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    <p class="mb-6">Now simply run the makefile with the following command.</p>

    <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>
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    <p class="mb-6">We have now successfully compiled the program with the help of a makefile. Now simply run the program and we'll
      see the output.</p>

    <div class="font-mono shadow-lg shadow-slate-500 p-2 mb-6">
<pre><code class="text-sm">
$ ./hello
 Hello, World!
</code></pre>
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    <p class="mb-6">The exact same should happen, if we run the next command instead.</p>

    <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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