Comparison of Pascal and Delphi: Difference between revisions

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{{Short description|Programming language}}

{{ProgLangCompare}}

{{use mdy dates|date=April 2023}}

Devised by [[Niklaus Wirth]] in the late 1960s and early 1970s, [[Pascal (programming language)|Pascal]] is a [[programming language]]. Originally produced by [[Borland]] Software Corporation, [[Embarcadero Delphi]] is composed of an IDE, set of standard libraries, and a Pascal-based language commonly called either [[Object Pascal]], Delphi Pascal, or simply 'Delphi' (Embarcadero's current documentation refers to it as 'the Delphi language (Object Pascal)'<ref>http://docwiki.embarcadero.com/RADStudio/XE2/en/Delphi_Reference</ref>). Since first released, it has become the most popular commercial Pascal implementation.

Devised by [[Niklaus Wirth]] in the late 1960s and early 1970s, [[Pascal (programming language)|Pascal]] is a [[programming language]]. Originally produced by [[Borland]] Software Corporation, [[Embarcadero Delphi]] is composed of an IDE, set of standard libraries, and a Pascal-based language commonly called either [[Object Pascal]], Delphi Pascal, or simply 'Delphi' (Embarcadero's current documentation refers to it as 'the Delphi language (Object Pascal)'<ref>{{Cite web|url=http://docwiki.embarcadero.com/RADStudio/XE2/en/Delphi_Reference|title = Delphi Reference - RAD Studio XE2}}</ref>). Since first released, it has become the most popular commercial Pascal implementation.

While developing Pascal, Wirth employed a [[Bootstrapping_Bootstrapping (compilers)|bootstrapping]] procedure in which each newer version of the Pascal compiler was written and compiled with its predecessor. Thus, the 'P2' compiler was written in the dialect compilable by 'P1', 'P3' in turn was written in 'P2' and so on, all the way till 'P5'. The 'P5' compiler implemented Pascal in its final state as defined by Wirth, and subsequently became standardardisedstandardised as 'ISO 7185 Pascal'.

The Borland dialect, like the popular [[UCSD Pascal]] before it, took the 'P4' version of the language as its basis, rather than Wirth's final revision. After much evolution independent of Standard Pascal, the Borland variant became the basis for Delphi. This page goes over the differences between Delphi and Standard Pascal. It does '''not''' go into Delphi-specific extensions to the language, which are numerous and still increasing.

== Exclusive features ==

== Differences between Standard Pascal and Delphi ==

Following features are mutually exclusive.

The Standard Pascal implementation is not accepted by Delphi and vice versa, the Delphi code is not acceptable in Standard Pascal.

=== Modulo with negative dividend ===

1. The way procedures and functions can be passed as parameters differs: Delphi requires explicit procedural types to be declared where Standard Pascal does not.

Standard Pascal has a Euclidean-like definition of the [[Modulo#In programming languages|<syntaxhighlight lang="pascal" inline>mod</syntaxhighlight> operator]] whereas Delphi uses a truncated definition.

=== Nested comments ===

2. Delphi does not support so called 'intraprocedural gotos', in which [[goto]] statements may reference targets outside the current procedure/function body.

Standard Pascal requires that the comment delimiters <syntaxhighlight lang="pascal" inline>{</syntaxhighlight> and the bigramm <syntaxhighlight lang="pascal" inline>(*</syntaxhighlight>, as well as <syntaxhighlight lang="pascal" inline>}</syntaxhighlight> and <syntaxhighlight lang="pascal" inline>*)</syntaxhighlight> are synonymous to each other.<ref name="gpc_comments"/>

In Delphi, however, a block comment started by <syntaxhighlight lang="pascal" inline>{</syntaxhighlight> ''must'' be closed with a <syntaxhighlight lang="pascal" inline>}</syntaxhighlight>.<ref name="moore"/>

The bigramm <syntaxhighlight lang="pascal" inline>*)</syntaxhighlight> will only close any comment that started with <syntaxhighlight lang="pascal" inline>(*</syntaxhighlight>.<ref name="moore"/>

This scheme allows for ''nested'' comments at the expense of compiler complexity.

=== Procedural data types ===

3. Standard Pascal has file 'buffer variables', together with 'get' and 'put' standard procedures that operate on them. Neither are supported in Delphi.

The way procedures and functions can be passed as parameters differs:

Delphi requires explicit procedural types to be declared where Standard Pascal does not.<ref name="reagan"/>

{| class="wikitable" style="margin: auto;"

|+ comparison procedural data types

|-

! Standard Pascal !! Delphi

|- style="vertical-align:bottom"

| <syntaxhighlight lang="pascal" highlight="3,4" style="font-size:85%">

program proceduralDataType(output);

{ `printYIntersect` has one procedural parameter: }

4. Given a variant record in Standard Pascal, the size of a particular variant can be specified. Delphi does not support this form of 'sized' dynamic variable allocation:

procedure printYIntersect(function f(x: real): real);

begin

writeLn(f(0.0));

end;

{ Standard Pascal does not have procedural “pointers.” }

function f(x: real): real;

begin

f := cos(x);

end;

{ ─── MAIN ───────────────────────────────────────────── }

begin

printYIntersect(f);

end.

</syntaxhighlight>

| <syntaxhighlight lang="delphi" highlight="1-4" style="font-size:85%">

type

TFunc = function(x: real): real;

procedure printYIntersect(f: TFunc);

<source lang="pascal">

begin

new(p, t) //where t is a variant record tag type; does not compile in Delphi

writeLn(f(0.0));

</source>

end;

function f(x: real): real;

5. The functions 'pack' and 'unpack' are not implemented in Delphi.

begin

f := cos(x);

end;

// ─── MAIN ─────────────────────────────────────────────

begin

printYIntersect(@f);

end.

</syntaxhighlight>

|}

=== Conversion of newline characters ===

6. The Delphi compiler does not treat { and (*, } and *) as synonyms like Standard Pascal requires. In other words,

Various computer systems show a wide variety how to indicate a [[newline]].

This affects the internal representation of <syntaxhighlight lang="pascal" inline>text</syntaxhighlight> files which are composed of a series of “lines”.

In order to relieve the programmer from any associated headaches, Standard Pascal mandates that ''reading'' an “end-of-line character” returns a single space character.

To distinguish such an “end-of-line” space character from a space character that is actually genuine payload of the line, <syntaxhighlight lang="pascal" inline>EOLn</syntaxhighlight> becomes <syntaxhighlight lang="pascal" inline>true</syntaxhighlight>.

Delphi does not show this behavior.

<source lang="pascal">

Reading a newline will return whatever character sequence represents a newline on the current host system, for example two <syntaxhighlight lang="delphi" inline>char</syntaxhighlight> values <syntaxhighlight lang="delphi" inline>chr(13)</syntaxhighlight> (carriage return) plus <syntaxhighlight lang="delphi" inline>chr(10)</syntaxhighlight> (line feed).<ref name="moore"/>

{ comment *)

</source>

== Additional or missing features ==

is not valid in Delphi. Instead, Delphi uses the scheme of allowing the different comment types to indicate nested comments.

Following features are present or missing in either language.

=== Global <syntaxhighlight lang="pascal" inline>goto</syntaxhighlight> ===

7. Delphi does not replace eoln with space as the Pascal standard requires. When reading through the end of a line, the eoln character is supposed to be replaced with a space in ISO 7185. Instead, reading through eoln in Delphi gives the character code for carriage return (13), followed by line feed (10).

Standard Pascal permits a <syntaxhighlight lang="pascal" inline>goto</syntaxhighlight> to any <syntaxhighlight lang="pascal" inline>label</syntaxhighlight> defined in scope.

In Delphi a <syntaxhighlight lang="delphi" inline>goto</syntaxhighlight> must be within the current routine, i. e. may not leave the <syntaxhighlight lang="delphi" inline>begin … end</syntaxhighlight>-frame.<ref name="moore"/>

<syntaxhighlight lang="pascal" highlight="6,7">program jumpAround;

label

999;

procedure foo;

begin

{ This is not permitted in Delphi: }

goto 999;

end;

begin

foo;

999: ;

end.</syntaxhighlight>

=== Buffer variables ===

8. Numbers and booleans are not printed out in their 'default' field widths by Delphi's version of the Write and WriteLn standard procedures, being instead printed in the minimum amount of space. For example, in Delphi,

Delphi does not support buffer variables and associated standard routines <syntaxhighlight lang="pascal" inline>get</syntaxhighlight> and <syntaxhighlight lang="pascal" inline>put</syntaxhighlight>.<ref name="moore"/>

<syntaxhighlight lang="pascal" highlight="5,6,15,19">program copy(input, output);

begin

while not EOF(input) do

begin

{ Copy file buffers. Not supported by Delphi }

output↑ := input↑;

{ Input↑ contains a space if a new-line occurred. }

if EOLn(input) then

begin

writeLn(output);

end

else

begin

put(output);

end;

{ Advance reading cursor. }

get(input);

end;

end.</syntaxhighlight>

=== Discriminated variant record allocation ===

<source lang="pascal">

In Standard Pascal allocating memory for a variant <syntaxhighlight lang="pascal" inline>record</syntaxhighlight> may indicate a specific variant.

write(5);

This allows implementations to allocate the least amount of ''really'' necessary memory.

write(55);

Delphi does not support this.<ref name="moore"/>

</source>

<syntaxhighlight lang="pascal" highlight="13,14">program variantRecord;

type

sex = (female, male);

clothingMeasures = record

girth: real;

case gender: sex of

female: (underbust: real);

male: ( );

end;

var

size: clothingMeasures;

begin

{ NB: No space allocated for `underbust`. }

new(size, male);

end.</syntaxhighlight>

=== Temporary files ===

is equivalent to:

In Delphi any file must be backed by a file in the file system.

That means any <syntaxhighlight lang="delphi" inline>file</syntaxhighlight> needs to be associated with a file name with Delphi's <syntaxhighlight lang="delphi" inline>assign</syntaxhighlight> procedure.

In contrast, Standard Pascal is usable without file names.

The following will produce a run-time error with Delphi.<ref name="moore"/>

<syntaxhighlight lang="pascal">program temporaryFile(output);

var

FD: text;

begin

rewrite(FD);

writeLn(FD, 'Hello world!');

end.</syntaxhighlight>

=== Packing ===

<source lang="pascal">

Delphi does not implement the standard procedures <syntaxhighlight lang="pascal" inline>pack</syntaxhighlight> and <syntaxhighlight lang="pascal" inline>unpack</syntaxhighlight>.<ref name="moore"/>

write(5:1);

Regardless, transferring data between packed and unpacked data types is an easy feat, although the implementation might not be as efficient as a compiler vendor supplied implementation would be.

write(55:2);

</source>

=== Missing default <syntaxhighlight lang="pascal" inline>write</syntaxhighlight> width ===

However, Standard Pascal requires it to be equivalent to the following (TotalWidth is implementation-defined):

Delphi does not associate the data type <syntaxhighlight lang="pascal" inline>Boolean</syntaxhighlight> with a default width if specified as <syntaxhighlight lang="pascal" inline>write</syntaxhighlight>/<syntaxhighlight lang="pascal" inline>writeLn</syntaxhighlight> parameters.<ref name="moore"/>

Delphi demonstrates the behavior as usual for character-strings.

=== Overloading ===

<source lang="pascal">

Delphi permits overloading routines.

write(5:TotalWidth);

In Standard Pascal identifiers must be unique in every block.

write(55:TotalWidth);

<syntaxhighlight lang="delphi">function f(x: integer): real;

</source>

begin

result := sin(x);

end;

function f(x: real): real;

Similarly, for booleans,

begin

result := cos(x);

end;

// ─── MAIN ─────────────────────────────────────────────

begin

// Note the different data types.

writeLn(f(3));

writeLn(f(3.0));

end.</syntaxhighlight>

=== Default parameter values ===

<source lang="pascal">

Delphi permits [[default parameter]]s.

write(false);

write(true);

</source>

== Peculiar implementation characteristics ==

is equivalent to

=== Standard <syntaxhighlight lang="pascal" inline>write</syntaxhighlight> width ===

In Pascal, if the destination file is a <syntaxhighlight lang="pascal" inline>text</syntaxhighlight> file, the parameters to <syntaxhighlight lang="pascal" inline>write</syntaxhighlight>/<syntaxhighlight lang="pascal" inline>writeLn</syntaxhighlight> have an implemention-defined default total width.

<source lang="pascal">

In Delphi, for <syntaxhighlight lang="delphi" inline>integer</syntaxhighlight> values this is simply <syntaxhighlight lang="delphi" inline>1</syntaxhighlight>.

write('false':5);

That means always the least amount of space is occupied.<ref name="moore"/>

write('true':4);

Other compilers have shown default widths of, for example, <syntaxhighlight lang="pascal" inline>20</syntaxhighlight> allowing for a fine tabular look at no cost of extra code.

</source>

{| class="wikitable" style="margin: auto;"

|+ comparison default <syntaxhighlight lang="pascal" inline>write</syntaxhighlight> width

in Delphi, but

|-

! colspan="2" | source code fragment

<source lang="pascal">

|-

write('false':TotalWidth);

| colspan="2" | <syntaxhighlight lang="pascal">writeLn(1);

write('true':TotalWidth);

writeLn(23456789);</syntaxhighlight>

</source>

|-

! colspan="2" | produces in

in ISO 7185.

|-

! Standard Pascal ([[GNU Pascal|GPC]]) !! Delphi

9. Temporary files are not supported by Delphi using traditional Pascal I/O - executing Reset() or Rewrite() results in an error, where under Standard Pascal it opens a temporary file that exists for the duration of the program before being automatically deleted.

|-

| <syntaxhighlight lang="text"> 1

10. Notwithstanding the fact Delphi still allows using much of the traditional Pascal RTL, Delphi-specific library functionality is generally implemented in ordinary Delphi code that uses, rather than adds to, compiler-provided intrinsics. This philosophy contrasts to Standard Pascal, whose RTL must be provided by the compiler. For example, in Standard Pascal, the 'file' type is an intrinsic type - sort of like a record, but another compiler-defined type alongside records. In contrast, the TFileStream class in Delphi is an ordinary Delphi class written in ordinary Delphi code. Similarly, the Read, ReadLn, Write and WriteLn standard procedures have signatures that are not themselves legal Pascal signatures. While Delphi still implements them, only vary rarely do Delphi-specific RTL routines require similarly special handling: rather, the language was evolved to include features such as 'open arrays', default parameters and procedural overloading that can be used by user-written routines too.

23456789</syntaxhighlight>

| <syntaxhighlight lang="text">1

23456789</syntaxhighlight>

|}

== References ==

<references>

<ref name="gpc_comments">{{cite web

<references />

| title = The GNU Pascal Manual

| first1 = Jan-Jaap

== See also ==

| last1 = van der Heijden

| first2 = Peter

* [[Delphi programming language]]

| last2 = Gerwinski

* [[Comparison of Pascal and C]]

| first3 = Frank

* [[Pascal (programming language)]]

| last3 = Heckenbach

| first4 = Berend

| last4 = deBoer

| first5 = Dominik

| last5 = Freche

| first6 = Eike

| last6 = Lange

| first7 = Peter

| last7 = Lewis

| display-authors = etal

| at = A QuickStart Guide from Borland Pascal to GNU Pascal

| url = https://www.GNU-Pascal.de/gpc/Comments.html#Comments

| access-date = 2023-04-24

}}</ref>

<ref name="reagan">{{cite web

| title = Pascal Standards FAQ

| at = Comparison of Borland Pascal to the Pascal standards

| first = John

| last = Reagan

| date = 1995-04-03

| url = http://Pascal-Central.com/extpascal.html#anchor-6

| archive-url = https://web.archive.org/web/20210928162340/http://pascal-central.com/extpascal.html#anchor-6

| archive-date = 2021-09-28

}}</ref>

<ref name="moore">{{cite web

| title = Standard Pascal FAQ

| at = Q. What are the differences between Borland Delphi and the ISO 7185 standard?

| first = Scott

| last = Moore

| date = 2022-12-02

| url = https://www.MooreCAD.com/standardpascal/pascalfaq.html#Q.%20What%20are%20the%20differences%20between%20Borland%20Del

| access-date = 2023-04-24

}}</ref>

</references>

== Further reading ==

* Kathleen Jansen and [[Niklaus Wirth]]: ''PASCAL - User Manual and Report.'' Springer-Verlag, 1974, 1985, 1991, {{ISBN |0-387-97649-3}}, {{ISBN |0-387-90144-2}}, and {{ISBN |3-540-90144-2}} [https://web.archive.org/web/20050314152247/http://www.cs.inf.ethz.ch/~wirth/books/Pascal/]

* Niklaus Wirth: ''The Programming Language Pascal.'' Acta Informatica, 1, (Jun 1971) 35-6335–63

* ISO/IEC 7185: ''Programming Languages - PASCAL.'' [http://www.moorecad.com/standardpascal/]

* Doug Cooper: ''Standard Pascal: User Reference Manual.'' W. W. Norton & Company, 1983, {{ISBN |0-393-30121-4}}, {{ISBN |978-0-393-30121-2}}

* Pascal standards documents [http://www.standardpascal.org/standards.html]

== External links ==

* [https://www.moorecad.com/standardpascal/ The ISO 7185 Pascal web site]

* [https://www.StandardPascal.org/standards.html Pascal standards documents]

{{Pascal programming language family}}

* The standard, ISO 7185 Pascal web site [http://www.moorecad.com/standardpascal/]

{{DEFAULTSORT:Pascal and Delphi comparison}}

[[Category:Pascal programming language family]]

[[Category:Borland]]

[[Category:ProgrammingComparison languageof comparisonsindividual programming languages]]

{{Pascal programming language family}}