Re: Variable declaration and while loops

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Mon, 18 Jun 2007 13:40:00 -0400

Message-ID:

<f56g1q$ka8$1@news.datemas.de>

Andre Kostur wrote:

"Victor Bazarov" <v.Abazarov@comAcast.net> wrote in news:f56981$8c8$1
@news.datemas.de:

Andre Kostur wrote:

"Victor Bazarov" <v.Abazarov@comAcast.net> wrote in
news:f562h2$sdg$1 @news.datemas.de:

Zachary Turner wrote:

Hello,

This seems like an extremely basic question, and I'm a bit
embarassed that I can't answer it myself.

I just recently started using GCC and tried to type the following
code:

while ((int i = getint()) != 0)

Drop the "!= 0" part and you'll have a standard construct.

Personal style: ick. I prefer to explicitly test against 0 when
dealing with ints (I also prefer to explicitly mention NULL when
dealing with pointers too.) If the expression type is bool (or
99.9% of the time intended to be treated as a bool, such as the
void* return of streams. It's not really intended to be used as a
pointer, but it prevents other unintentional implicit type
conversion.), then I'll do the implicit test.

Yes, as a matter of style I like seeing ints tested explicitly
against zero, but for pointers I like saying 'if (pointer) '. The
syntax is also very convenient for streams (both C and C++), where
you don't care for the variable to survive beyond the point of check.

Compare

    if (FILE* blah = fopen("somename", "rb")) {
        // do something with 'blah'
    }

and

    {
        FILE* blah = fopen("somename", "rb");
        if (blah != NULL) {
            // do something with 'blah'
        }
    }

Did you notice the extra pair of braces? Ick! Besides, the former
code reads better, IMNSHO. "If file opens, do something", compared
to "open blah. if blah is not NULL ..." [..Wait a minute? Why am I
checking for NULL when the term should be "opens"? so now I need to
introduce an extra utility function or macro:

Yep... but hopefully your function is small enough that the FILE* has
the scope of the entire function anyway. (Or suffer with a FILE*
that has a larger scope than strictly necessary).

Why suffer?

    inline bool opened_OK(FILE* f) { return f != NULL; }

and write

    {
        FILE* blah = fopen("somename", "rb");
        if (opened_OK(blah)) {
            // do something with 'blah'
        }
    }

This would be the pain of using C-style functions :) Use streams :)

Goes the same way

    if (std::ifstream blah("somename", ios::binary)) {
        // do something with blah
    }

Works like a charm with any C++ objects that define operator void* or
operator bool to indicate "good state".

Ick!]

See my point?

Sure... the style doesn't work for you. Arguably if you need to add
additional braces, perhaps you should consider refactoring that piece
of code into its own function.

Nope. I have a perfectly working language construct that I use instead.

V
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