Re: Block Comments Or Rest-Of-Line Comments?

On 21/03/2024 17:32, Richard Harnden wrote:

On 21/03/2024 15:20, David Brown wrote:

On 21/03/2024 07:19, Lawrence D'Oliveiro wrote:

The original comment delimiters in C were copied from PL/I: everything
between “/*” and “*/” is a comment, even extending across multiple lines.
Pascal had something similar, only the delimiters were “{” and “}”, or
“(*” and “*)” for compatibility with machines with restricted character
sets.
>
For some reason, the Ada folks decided block comments were not a good
idea, and so their rule was that anything after “--” up to the end of the
line was a comment. And C++ adopted a similar rule, using “//” as their
to-end-of-line comment marker, though of course they also kept C-style
block comments. Java also keeps both these styles.
>
Since then, I’ve seen newer programmers gravitate towards the rest-of-line
form in preference to the block form, and I’m not sure why. I’m fond of
writing things like
>
/*
     A very simple HTML/XML entity-escape function--why isn’t this
     part of the standard Java API?
*/
>
which involve less typing than
>
//
//  A very simple HTML/XML entity-escape function--why isn’t this
//  part of the standard Java API?
//
>

>
I use both - block comments when making a comment block, and line comments when adding comments to the end of a line.  That seems pretty obvious to me.

 And sometimes, when it's not a really a comment, but rather a block of code I don't want right now:
 #ifdef 0

"#if 0", presumably.

...
#endif
 

Yes, I do that too.  But if it is more than just a fairly trivial amount of code, and not just for quite tests during development, then I hugely prefer to give the block a name:
// Explanation of EnableExtraChecks ...
#define EnableExtraChecks 1
...
#if EnableExtraChecks
...
#endif // #if EnableExtraChecks
Depending on the circumstances, the guard macro definition might be at the start of the file, or it might be just before the commented-out block.  But even in the later case, giving it a name like this makes it easier to match up when the #endif (and perhaps #else) has a comment. It also makes it easier to get right if there are several blocks that get commented out, whether they use the same or different guards.
Note that some coding standards (such as MISRA) do not allow this technique, because it can be hard (without a good highlighting editor or IDE) to see if code is active or disabled.