- Comparison of Pascal and Delphi
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This article is a comparison between Pascal and Delphi because Borland, the original manufacturer of Delphi, once used Delphi for their version of the Pascal-based programming language used in the product, which is otherwise known as Object Pascal. Compatibles still maintain the Object Pascal designation because Delphi is a registered trademark.
Pascal is a programming language, developed in 1970 by Niklaus Wirth. The original Pascal employed a bootstrapping construct where each successively more complicated compiler compiled the next iteration. Thus the compiler P2 was written in the dialect compilable by P1, and could in turn compile P3, and such on all the way till P5 which implemented "full" Pascal and was more optimized.
Borland Corporation, like the wildly popular UCSD Pascal before them, took the P4 subset compiler as their basis for their Turbo Pascal range, probably because they considered it more efficient on the micros they were targeting. Over time their dialect implemented many UCSD extensions to the original Pascal like the "string" type. Their language went through several versions and names, such as Turbo Pascal, Borland Pascal, and finally Delphi Pascal. This page briefly goes over the differences between those dialects of the language. It does not go into the extensions provided by Delphi, that is the subject of a Delphi page. Rather it just covers the differences that exist between the base implementations.
Contents
Terminology
It is correct to refer to "Pascal" in general as Niklaus Wirth's original language (and derivatives) and Borland's dialect as "Delphi". When referring to Borland's previous dialects, the terms "Turbo Pascal", and "Borland Pascal" apply.
The term "ISO 7185" or "ISO 7185 Pascal" is used here as synonymous with Niklaus Wirth's programming language Pascal. The ISO 7185 standard is the standardized version of Niklaus Wirth's language, as he has stated several times.
Differences between the languages
Because Borland Delphi is a widely used version of Pascal, it is useful to compare the two languages. Note that here are presented only the differences between Borland Delphi and the basic ISO 7185 standard. Undiscussed are any extensions provided by Borland Delphi. In other words, this section answers the question "why doesn't my standard Pascal program run under Borland Delphi?", and perhaps "what can I write in Borland Delphi that will also be compatible with the ISO 7185 standard?".
1. Procedures and functions may not appear as parameters (it is true that it can be done, but a non-standard syntax must be used).
2. Goto statements cannot reference targets outside procedure/function bodies (so called "intraprocedural gotos").
3. No file buffer variable handling. Standard Pascal has file "buffer variables", and "get" and "put" procedures to operate on them. This functionality is not present in Borland Delphi.
4. No "sized" dynamic variable allocation. Given a variant record, the size of a particular variant cannot be specified as per the standard. I.e., the following statement is invalid:
new(p, t)
Where t is a variant record tag type.
5. The functions "pack" and "unpack" are not implemented.
6. { and (*, } and *) are not synonyms of each other as required by the standard. I.e.:
{ comment *)is not valid in Borland Delphi (Delphi uses the scheme of allowing the different comment types to indicate nested comments). It is valid in Turbo Pascal though.
7. Does not replace eoln with space as the 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 Borland Delphi gives the character code for carriage return (13), followed by line feed (10).
8. Numbers and booleans are not printed out in their "default" field widths, but are printed in the minimum amount of space. For example:
write(5); write(55);
is equivalent to:
write(5:1); write(55:2);
in Delphi, but:
write(5:TotalWidth); write(55:TotalWidth);
in ISO 7185, where TotalWidth is implementation-defined.
For booleans:
write(false); write(true);
is equivalent to:
write('false':5); write('true':4);
in Delphi, but:
write('false':TotalWidth); write('true':TotalWidth);
in ISO 7185, where TotalWidth is implementation-defined.
9. Temporary files are not supported. Executing reset() or rewrite() results in an error under Delphi. Under standard Pascal it opens a temporary file that exists only for the run of the program.
See also
- Delphi programming language
- Comparison of Pascal and C
- Pascal (programming language)
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 [1]
- Niklaus Wirth: The Programming Language Pascal. Acta Informatica, 1, (Jun 1971) 35-63
- ISO/IEC 7185: Programming Languages - PASCAL. [2]
- Doug Cooper: Standard Pascal: User Reference Manual. W. W. Norton & Company, 1983, ISBN 0393301214, ISBN 9780393301212
- Pascal standards documents [3]
External links
- The standard, ISO 7185 Pascal web site [4]
Dialects 
Compilers CurrentDelphi · Delphi Prism (Oxygene) · PocketStudio · HP Pascal · IP Pascal · Prospero Pascal · C/AL · Free Pascal (Lazarus) · GNU Pascal · Turbo51 · Virtual Pascal · MIDletPascal · Pic Micro Pascal · ACKHistoricalCategories:- Pascal programming language family
- Borland
- Programming language comparisons
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