Size of UTF-8 string in bytes - c++

Question

I am using QString to store strings, and now I need to store these strings (converted to UTF-8 encoding) in POD structures, which looks like this :
template < int N >
struct StringWrapper
{
char theString[N];
};
To convert raw data from the QString, I do it like this :
QString str1( "abc" );
StringWrapper< 20 > str2;
strcpy( str2.theString, str1.toUtf8().constData() );
Now the question. I noticed that if I convert from normal string, it works fine :
QString str( "abc" );
std::cout<< std::string( str.toUtf8().constData() ) << std::endl;
will produce as the output :
abc
but if I use some special characters, like for example :
QString str( "Schöne Grüße" );
std::cout<< std::string( str.toUtf8().constData() ) << std::endl;
I get a garbage like this:
Gr\xC3\x83\xC2\xBC\xC3\x83\xC2\x9F
I am obviously missing something, but what exactly is wrong?
ADDITIONAL QUESTION
What is a maximum size of an UTF-8 encoded character? I read it here it is 4 bytes.

Answer 1

The first question you need to answer is what is the encoding of your source files is? QString default constructor assumes it's Latin1 unless you change it with QTextStream::setCodecForCStrings(). So if your sources are in anything else than Latin1 (say, UTF-8), you get a wrong result at this point:
QString str( "Schöne Grüße" );
Now, if your sources are in UTF-8, you need to replace it with:
QString str = QString::fromUtf8( "Schöne Grüße" );
Or, better yet, use QObject::trUf8() wherever possible as it gives you i18n capabilities as a free bonus.
The next thing to check is what is the encoding of your console is. You try to print a UTF-8 string to it, but does it support UTF-8? If it's a Windows console, it probably doesn't. If it's something xterm-compatible using a Unicode font on a *nix system with some *.UTF-8 locale, it should be fine.
To your edited question:
I don't see any reason not to trust Wikipedia, especially when it refers to a particular standard. It also mentions that UTF-8 used to have up to 6 bytes characters, though. From my experience, 3 bytes is maximum you get with reasonable native language characters like Latin/Cyrillic/Hebrew/Chinese/Japanese. 4 bytes are probably used for something much more exotic, you can always check the standards if you are really curious.

Answer 2

The first thing that goes wrong is your stated assumption. QString doesn't store UTF-8, it stores unicode strings. That's why you need to call str1.toUtf8(). It creates a temporary UTF-8 string.
The second part is just how UTF-8 works. It's a multi-byte extension of ASCII. üß aren't ASCII characters, and you do expect that both characters get a multi-byte representation. std::cout apparently doesn't expect UTF-8. This depends on the std::locale used.