Re: Stream state question

From:
"Alf P. Steinbach" <alfps@start.no>
Newsgroups:
comp.lang.c++
Date:
Sun, 30 Sep 2007 00:40:33 +0200
Message-ID:
<13ftl37tf4trn40@corp.supernews.com>
* john:

In TC++PL 3, on page 616, "class basic_ios" has the public members

"operator void *() const; // nonzero if !fail()
 bool operator!() const { return fail(); }"

for using them in conditional statements in the style:

if(cin) // if( !void *(0) )

if(!cin) // if( cin.operator!()

Why isn't operator bool() used instead? For historical reasons?


The implicit conversion with operator bool() would allow things like
passing a stream object to int formal function argument.

The implicit conversion with void* is more narrow in what it can match.

However, the worst problem with implicit conversions is that they are
not explicit -- you can't see them from reading the program text.

So one relevant question is, why is there an implicit conversion at all?

And for that, I have no other answer than that iostreams are not in
general examples of best practice as regards design: they just evolved
from some practical small early classes, into impractical huge beasts.

Cheers, & hth.,

- Alf

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