what's wrong with the macro

[DaVinci]

#include<stdio. h>
#include<stdlib .h>
#include<string .h>

#define SECONDS_PER_YEA R (60*60*24*365)U L
int main()
{
unsigned long int u_i = SECONDS_PER_YEA R;
printf("%lu\n", u_i);

return 0;
}
cc -g -c -Wall -std=c99 -DDEBUG define.c
define.c: In function 'main':
define.c:17: error: expected ',' or ';' before 'UL'
make: *** [define.o] error 1

[Richard Tobin]

In article <8e************ *******@news.in digo.ie>,
Frederick Gotham <fg*******@SPAM .comwrote:

>I'd like to ask any other programmers to explain to me why:

sizeof (unsigned long)(60UL * 60UL * 24UL * 365UL)

would have been undesireable.

Because it's a syntax error.

>The expression in question has only one possible parse, because the operand
of "sizeof" cannot be a cast expression.

It has no possible parses.

>Therefore, the following two
expressions are exactly equivalent:

sizeof (unsigned long)(60UL * 60UL * 24UL * 365UL)

sizeof ((unsigned long)(60UL * 60UL * 24UL * 365UL))

No, one of them's an error and the other one isn't.

-- Richard

[Frederick Gotham]

Richard Tobin posted:

> sizeof (unsigned long)(60UL * 60UL * 24UL * 365UL)

Because it's a syntax error.

So you can turn a cast expression into a normal expression (or whatever it's
called) by enclosing it in parentheses?

--

Frederick Gotham

[Richard Tobin]

In article <JJ************ *******@news.in digo.ie>,
Frederick Gotham <fg*******@SPAM .comwrote:

>So you can turn a cast expression into a normal expression (or whatever it's
called) by enclosing it in parentheses?

Yes, it becomes a primary expression (IIRC - I don't have the grammar
handy). That's the basic way of making the grammar handle arbitrarily
complicated expressions: by putting a subexpression in parentheses it
becomes usable in the same contexts as numbers and strings.

-- Richard

[Chris Dollin]

Frederick Gotham wrote:

Richard Tobin posted:

>> sizeof (unsigned long)(60UL * 60UL * 24UL * 365UL)

Because it's a syntax error.

So you can turn a cast expression into a normal expression (or whatever it's
called) by enclosing it in parentheses?

Looking at the grammar ...

The operand of a `sizeof` must be a unary-expression. A unary-expression
can be a postfix-expression, which can be a primary-expression, which can
be any expression enclosed in parentheses.

So yes, parenthesising a cast-expression makes it suitable as an
operand of `sizeof`.

I wouldn't have thought this was surprising: putting bracketty things
around big wobbly expresssions to make them into snug tight expressions
is a common grammatical trick, eg `2 * (20 + 1)`.

--
Chris "common, but not universal" Dollin
A rock is not a fact. A rock is a rock.

[Clark S. Cox III]

Frederick Gotham wrote:

Richard Tobin posted:

>> sizeof (unsigned long)(60UL * 60UL * 24UL * 365UL)

Because it's a syntax error.

So you can turn a cast expression into a normal expression (or whatever it's
called) by enclosing it in parentheses?

Of course you can it's spelled out pretty clearly in the grammar. Any
'expression' enclosed in parentheses is a 'primary-expression':

(6.5.1)primary-expression:
identifier
constant
string-literal
( expression )

And a 'cast-expression' is a 'multiplicative-expression'
which is, in turn an 'additive-expression'
which is, in turn a 'shift-expression'
which is, in turn a 'relational-expression'
which is, in turn an 'equality-expression'
which is, in turn an 'AND-expression'
which is, in turn a 'exclusive-OR-expression'
which is, in turn a 'inclusive-OR-expression'
which is, in turn a 'logical-AND-expression'
which is, in turn a 'logical-OR-expression'

which is, in turn a 'conditional-expression'
which is, in turn a 'assignment-expression'
which is, in turn an 'expression'

*pant* *pant* *pant*
--
Clark S. Cox III
cl*******@gmail .com

[Mark McIntyre]

On Tue, 24 Oct 2006 15:23:48 GMT, in comp.lang.c , Frederick Gotham
<fg*******@SPAM .comwrote:

>Since the two self-proclaimed masters of this newsgroup won't reply to me,

Lets all recall that the reason these (and other) regulars don't reply
is because you're offensive. Nobody can be bothered.
--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

[CBFalconer]

Frederick Gotham wrote:

Keith Thompson posted:

<snip tripe>

Richard Heathfield posted:

<snip tripe>

Since the two self-proclaimed masters of this newsgroup won't reply
to me, I'd like to ask any other programmers to explain to me why:

Well, I haven't gone quite that far, but the fact is that you know
very well how to repair that situation. You have chosen not to do
so for your own incomprehensibl e reasons, and continue to insult
them. I suspect many others are ignoring you without advising you
of the fact.

Enjoy Coventry.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net>

[Keith Thompson]

Richard Heathfield <in*****@invali d.invalidwrites :

Keith Thompson said:

>Frederick Gotham <fg*******@SPAM .comwrites:

>>Keith Thompson posted:
You want parentheses around the second defintion:

#define SECONDS_PER_YEA R ((unsigned long)(60UL * 60UL * 24UL * 365UL)(

Consider "sizeof SECONDS_PER_YEA R".

I don't understand... what could that have parsed to?

Frederick, I don't want to leave you waiting for a response from me,
so I'll remind you of this:

<http://groups.google.c om/group/comp.lang.c/msg/a03c532b26664ed 4>

A waste of time, Keith. If he were interested in responses from you, he'd
have apologised a long time ago.

I'm not waiting for, or expecting, an apology from him. See the
article I cited if you care (but there's no real reason you should).
I wasn't trying to elicit any particular response from him, just
reminding him that he shouldn't expect one from me.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Christopher Benson-Manica]

Keith Thompson <ks***@mib.orgw rote:

You want parentheses around the second defintion:

^^^^^^^^^

#define SECONDS_PER_YEA R ((unsigned long)(60UL * 60UL * 24UL * 365UL)(

Did you mean

#defin SECONDS_PER_YEA R ((unsigned long)(60UL * 60UL * 24UL * 365UL))

or was that a typo too? :-)

--
C. Benson Manica | I *should* know what I'm talking about - if I
cbmanica(at)gma il.com | don't, I need to know. Flames welcome.

[Keith Thompson]

Christopher Benson-Manica <at***@otaku.fr eeshell.orgwrit es:

Keith Thompson <ks***@mib.orgw rote:

>You want parentheses around the second defintion:

^^^^^^^^^

>#define SECONDS_PER_YEA R ((unsigned long)(60UL * 60UL * 24UL * 365UL)(

Did you mean

#defin SECONDS_PER_YEA R ((unsigned long)(60UL * 60UL * 24UL * 365UL))

or was that a typo too? :-)

Yes, taht wsa a tpyo. :)-

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.