🚀 go-pugleaf

In article kgn@mulga.cs.mu.OZ.AU, fjh@munta.cs.mu.OZ.AU (Fergus Henderson) writes:
>clamage@Eng.Sun.COM (Steve Clamage) writes:
>>
>>Yes, you forgot to say how it differs from #error, which is already in the
>>draft (and in Standard C). The description of #error says only that it
>>"causes the implementation to produce a diagnostic message that includes
>>the specified sequence of preprocessing tokens."
>
>Isn't this a bug in the standard?  Doesn't this mean that
>
>	#error foobar
>	int main() { return 0; }
>
>is a strictly conforming program?  Yet no compiler I know of will accept it!

It is a strictly conforming program (although we don't use that terminology
in the C++ standard). The implementation must tell you what the effect
of #error is. If the effect is to abort compilation, that is allowed.

>Surely the semantics specified for #error should say that it has the effect
>of making the translation unit ill-formed.

Why? You can write ill-formed code if you want to. For example:
	#if undesirable_condition
	this phrase should not be seen by the compiler
	#endif

The #error directive is part of the language, and I think it would be a
contradiction in terms to say that a valid language construct is ill-formed.

"Everyone knows" that the #error directive is supposed to halt compilation,
but for reasons I outlined earlier there isn't a good way (or at least
no one has found a way) to say so in the standard, given the basic
assumptions about what the C++ standard is supposed to be. Other languages
may define a particular environment where you can talk about compilation,
or linking, or known formats of data types, etc, but we have chosen not
to do so with C++.
---
Steve Clamage, stephen.clamage@eng.sun.com



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