Talk:Comments

Pascal Comments

The Pascal section claims that '{' and '}' are Turbo Pascal extensions. However the Pascal Standard, ISO/IEC 7185:1990 explicitly contains:

6.1.8 Token separators

Where a commentary shall be any sequence of characters and separations of lines, containing neither

} nor *), the construct

( `{' | `(*' ) commentary ( `*)' | `}' )

shall be a comment if neither the { nor the (* occurs within a character-string or within a commentary.

NOTES

1 A comment may thus commence with { and end with *), or commence with (* and end with }.

2 The sequence (*) cannot occur in a commentary even though the sequence {) can.

Therefore { and } are comment delimiters in standard pascal. Note that comments like

(* this }

or

{ this *)

are valid Standard Pascal comments, but not valid Turbo Pascal comments.

Another interesting quote from the standard:

6.1.9 Lexical Alternatives

[...]

The comment-delimiting characters { and } shall be the reference representations, and (* and *)

respectively shall be alternative representations (see 6 .1 .8).

I guess it couldn't be more explicit :-) --Ce

Thanks for the clarification! I guess my memory was faulty. Personally, I always used { } in Turbo Pascal. --IanOsgood 18:33, 29 September 2007 (MDT)

C: #if 0 and syntax errors

The assertion was made that

#if 0
This isn't valid.	 
#endif

would cause a compile error due to an unmatched apostrophe in a character literal. This is false. The preprocessor removes this text from the source before the compiler has a chance to parse it. --IanOsgood 18:59, 29 September 2007 (MDT)

Did you actually read the text you removed? The Compiler does not see the unterminated character constant, but the Preprocessor does. See e.g. http://c-faq.com/ansi/ifdefsyntax.html

Unfortunately I don't have the C standard, so I cannot quote directly from there, but I double-checked with C++ that both CD2 (latest public draft of the 1998 version) and n2009 (a draft for the next section) contain wording identically in both (i.e. with exrtemely high probability also in the real standard) that this is true in C++ as well. More exactly, character literals are preprocessing tokens, and translation to preprocessing tokens happens in translation phase 3, while processing of preprocessing directives (this includes #ifdef) doesn't happen until translation phase 4. --Ce 05:17, 30 September 2007 (MDT)