At 12:52 PM -0800 2/9/09, Clark Cox wrote:
On Mon, Feb 9, 2009 at 12:10 PM, Sean McBride <s...@rogue-research.com> wrote:
> On 2/9/09 11:24 AM, Clark Cox said:
>>That is, the preprocessor treats any undefined identifier in an '#if'
or '#elif" as if it were defined to be zero.
> I'm not a language lawyer, but I believe the latter is not guaranteed to
evaluate to 0 if the macro is not defined. However, I imagine 99% of
compilers will evaluate it to 0. gcc certainly does.
I am 100% positive that this is guaranteed by the standard:
From 6.10.1.3:
"After all replacements due to macro expansion and the defined unary
operator have been performed, all remaining identifiers are replaced
with the pp-number 0"
Just to be pedantic, which standard?
You are definitely describing the behavior of the C++ preprocessor.
IIRC, in ANSI C, #if of an undefined symbol is an error, and I'm not
sure about C99.
So, I belive #if defined(x) && (x) is good defensive programming.
-Steve
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