Re: Writing unsigned char to std::ostream

David Wilkinson <>
Mon, 03 Sep 2007 17:54:06 -0400
Giovanni Dicanio wrote:

"David Wilkinson" <> ha scritto nel messaggio

Christof Meerwald wrote:

Why don't you use:

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

or even

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


Because it seems it is not guaranteed to work.

David: it seems just fine (both compile and run) on both Windows and Kubuntu
(g++) ...

I don't understand the problem...


I don't think it is a compiler issue so much as a hardware issue. Both
Windows and Kubuntu run on Intel platform, which has "sane" behavior.

But there are (apparently) systems where

char c = 0xFF;

creates a value that tests equal to 127. On such systems, it seems to
me, the BOM will not be written correctly. But Uli's method

unsigned char const utf8_bom[] = { 0xef, 0xbb, 0xbf, 0};
ostrm << utf8_bom << header << std::endl;

will work, because the bits in the individual characters are not changed
by the implementation of ostream::operator <<() for const unsigned char*
(which just casts to const char*).

David Wilkinson
Visual C++ MVP

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