Re: Writing unsigned char to std::ostream

From:

"Ben Voigt [C++ MVP]" <rbv@nospam.nospam>

Newsgroups:

microsoft.public.vc.language

Date:

Tue, 4 Sep 2007 17:08:36 -0500

Message-ID:

<uvuYZA07HHA.1208@TK2MSFTNGP05.phx.gbl>

"David Wilkinson" <no-reply@effisols.com> wrote in message
news:eJSfQlu7HHA.1188@TK2MSFTNGP04.phx.gbl...

David Wilkinson wrote:

Christof Meerwald wrote:

On Sun, 02 Sep 2007 12:37:44 -0400, David Wilkinson wrote:

In my MFC project I have a piece of code like

void XMLHelper::WriteHeader(std::ostream& ostrm)
{
   ostrm.put(unsigned char(0xEF)); // 1
   ostrm.put(unsigned char(0xBB));
   ostrm.put(unsigned char(0xBF));

Why don't you use:

ostrm << '\xef' << '\xbb' << '\xbf';

or even

ostrm << "\xef\xbb\xbf";

Christof:

Because it seems it is not guaranteed to work.

Christof:

My apologies. I missed the crucial distinction between "hexadecimal
constants" and "hexadecimal character constants".

I'm sure the history of this fiasco is that originally I tried

ostrm.put(0xEF);

and got integer truncation warnings. This caused me to do

ostrm.put(unsigned char(0xEF));

A big, BIG, mistake, which caused me to get involved with compound type
name issues and integer conversion issues. What I should have done was

ostrm.put('\xEF');

Nothing wrong with this, I think, but for a text file perhaps operator
<<() would be better, as you suggest.

I think put() is better than operator<< for this, because operator<<, when
passed a non-ASCII character such as you have, might do multibyte encoding
in some environments!

I always knew that if I was taken out of my ASCII/8 bit char/2's
complement-centric world then things might get ugly, and I was right!

Thanks again. Hexadecimal character constants. Got it now.

--
David Wilkinson
Visual C++ MVP