Sabtu, 02 Februari 2008

Differences between the languages Borland Delphi

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. Ie.:

{ comment *)

is not valid in Borland Delphi (Delphi uses the scheme of allowing the different comment types to indicate nested comments).

7. It is not possible to construct a standard program without compiler directives. At minimum:


is required.

8. 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).

9. 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, '<');



in Delphi, but:

> 5<

(spaces depend on compiler integer width) in ISO 7185.

For booleans:

write('>', true, '<');



in Delphi, but:

> true<

In ISO 7185.

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