Re: K&R Exercise 6-2

[August Karlstrom]

Richard Heathfield wrote:
[...]

In C90, an implementation must be able to distinguish between external
identifiers that are unique in the first 6 characters (without regard to
case!). A program such as the one required in Exercise 6-2 could be useful
for diagnosing source code that ignores this limit (as I suspect a vast
amount of source code does).

So a library which exports e.g. the identifiers string_prepend and
string_append are not really C90 compliant?
August

[Harald van =?UTF-8?b?RMSzaw==?=]

On Fri, 29 Aug 2008 16:51:56 +0200, August Karlstrom wrote:

Richard Heathfield wrote:
[...]

>In C90, an implementation must be able to distinguish between external
identifiers that are unique in the first 6 characters (without regard
to case!). A program such as the one required in Exercise 6-2 could be
useful for diagnosing source code that ignores this limit (as I suspect
a vast amount of source code does).

So a library which exports e.g. the identifiers string_prepend and
string_append are not really C90 compliant?

Correct. However, they are already not C90 compliant -- and not C99
compliant either -- for another reason: external identifiers starting with
str and followed by a lowercase letter are reserved for the implementation.

[Richard Heathfield]

August Karlstrom said:

Richard Heathfield wrote:
[...]

>In C90, an implementation must be able to distinguish between external
identifiers that are unique in the first 6 characters (without regard to
case!). A program such as the one required in Exercise 6-2 could be
useful for diagnosing source code that ignores this limit (as I suspect
a vast amount of source code does).

So a library which exports e.g. the identifiers string_prepend and
string_append are not really C90 compliant?

Right, for two reasons:

(1) the names invade implementation namespace;
(2) the names are a touch on the long side.

In practice, (1) is often ignored, and (2) is practically always ignored.
But strictly speaking, yes, you are correct.

Of the two reasons, (1) is probably the more important. Whilst it is
certainly possible that some people are still using 6-sig-char linkers
nowadays, it isn't terribly likely that terribly many people are. Even
twenty years ago (and probably more), people were ignoring the 6-character
thing, and it doesn't seem to have caused any major software crises.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[August Karlstrom]

Harald van Dijk wrote:

On Fri, 29 Aug 2008 16:51:56 +0200, August Karlstrom wrote:

>Richard Heathfield wrote:
[...]

>>In C90, an implementation must be able to distinguish between external
identifiers that are unique in the first 6 characters (without regard
to case!). A program such as the one required in Exercise 6-2 could be
useful for diagnosing source code that ignores this limit (as I suspect
a vast amount of source code does).

So a library which exports e.g. the identifiers string_prepend and
string_append are not really C90 compliant?

Correct. However, they are already not C90 compliant -- and not C99
compliant either -- for another reason: external identifiers starting with
str and followed by a lowercase letter are reserved for the implementation.

Annoying. Is there a way to make a compiler like GCC emit a warning in
this case?
August

[August Karlstrom]

Richard Heathfield wrote:

August Karlstrom said:

>So a library which exports e.g. the identifiers string_prepend and
string_append are not really C90 compliant?

Right, for two reasons:

(1) the names invade implementation namespace;
(2) the names are a touch on the long side.

In practice, (1) is often ignored, and (2) is practically always ignored.
But strictly speaking, yes, you are correct.

Of the two reasons, (1) is probably the more important. Whilst it is
certainly possible that some people are still using 6-sig-char linkers
nowadays, it isn't terribly likely that terribly many people are. Even
twenty years ago (and probably more), people were ignoring the 6-character
thing, and it doesn't seem to have caused any major software crises.

Thanks for the clarification.
August