|A Free Pascal Compiler
A recent venture
into programming (see the earlier newsletter article Back to
Basics) using a language that I initially thought I knew
something about turned into a research project on a very different,
object-oriented variant. I came across a reference to Free Pascal,
seemingly a version of yet another language I have used previously.
So, attracted by the combination of “free” (my favourite category
of software) and “Pascal”, I decided to take a look at this
open-source Pascal compiler.
for Free Pascal indicates that it supports multiple hardware
platforms and operating systems. In particular, it will support 32-
and 64-bit Windows and Linux which, potentially, makes it a useful
tool for my purposes.
I didn’t find
downloading the installation package all that intuitive. On the
download page of Free Pascal’s web site, I selected AMD64/Intel
64/x86_64, Windows 64-bit, and SourceForge as the mirror, and was
confronted by a number of packages. These included
fpc-3.0.4.i386-win32.cross.x86_64-win64.exe. Now, while the latter
package appears to be related to 64-bit systems, Windows indicated
that the installed Free Pascal Compiler (fpc) was not compatible with
my 64-bit operating system. It turned out that I needed to install
fpc-3.0.4.i386-win32.exe, after which fpc ran quite happily.
I opted to install the compiler in C:\FPC. The program is then
activated by running C:\FPC\3.0.4\bin\i386-win32\fp.exe. The display
is interesting. The compiler essentially opens in a command window,
and displays (on my system at least) an extremely pixelated “FPC”
graphic. More importantly, there is a File, Edit, Search, Run…
menu bar running across the top of the window. This DOS-type menu
system is FreePascal’s Integrated Development Environment (IDE).
The IDE provides the
tools that we need to create, edit, save, compile and run our Pascal
programs. It displays multiple windows such as a text-entry screen
in which we can enter the Pascal source code, and a window in which
messages (e.g. errors) from the compiler are reported.
Our first task is to
establish contact with an existing data folder (D:\FreePascal) in
which we are going to store our source code. Click on File and
select the Change dir… option to display the default directory
tree. The easiest way to get to our existing folder is to navigate
to Drives, double-click to show the available drives, double-click on
D, and finally double-click on the FreePascal folder. Now click on
the Ok button in the dialogue box to make D:\FreePascal the active
directory. (And, that was the easiest way!)
Now, we select File
– New and, thinking back to our Turbo Pascal days, we type in the
five lines of code for the infamous “Hello world” program. We
can use File – Save to store this as the source file hello.pas.
Selecting the Compile item from the main menu allows us to choose the
Compile option. If there are no mistakes in our typing (or in our
memory!), the compiler will return the message “Compile successful:
Press any key”.
that we forgot that the “Hello world” writeln statement must end
with a semi-colon. Now, when the source code is compiled, two
message windows will pop-up. One of these, labelled Compiling (Debug
mode) will tell us that there are 2 errors and that “Compile
failed”; the second window, labelled “Compiler Messages” will
Fatal: Syntax error “;” Expected but “identifier READLN”
The (4,3) portion of
the error message tells us that the error is on line 4 in column 3.
This seems to indicate that the syntax of the readln statement is at
fault. However, the error message also indicates that FreePascal is
expecting a semi-colon but it found readln instead. Perhaps this is
a clue! There is no semi-colon on line 3. We can fix any such
errors in the source code window and click on the small green square
in each of the error-message windows to remove them from the display.
Once we have successfully compiled the program, we are left with our
source code visible in the editor. In the background, FreePascal has
created the files hello.o (the object file) and hello.exe, the
executable program. If we navigate to D:\FreePascal in File Explorer
and double-click on hello.exe, a command window opens and “Hello
world” is displayed. Success!
Note that we can
also run the program by selecting Run from FreePascal’s menu, and
then selecting the Run option. The IDE changes to a command window
To return to the
IDE, we simply (but non-intuitively) hit the Enter key.
So, we know a few of
the basics of how to create, compile, and run FreePascal programs.
Now the trick is to produce a program that will do something useful!
However, before we move on to such heady tasks, we will take a small
detour to explore a somewhat more sophisticated version of the IDE –
a package named Lazarus. But, this will have to wait for Part 2 in
Free Pascal (Open
published: January 2019
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