What tools in Qt are there to decode HTML 4 entities? - qt

Question

I have an input QString that has HTML 4 entities, like õ that I’d like to decode. But I can’t find any facilities in Qt to do so. Is there a way to do so in Qt? If possible I’d like to avoid QTextDocument so I don’t have to bring in QtGui.
The HTML 4 entities are listed in this link:
https://www.w3schools.com/charsets/ref_html_entities_4.asp

Answer 1

Out of curiosity, I have looked a bit around.
I found this SO: How can i convert entity character(Escape character) to HTML in QT?. However, it uses QTextDocument (which is part of GUI) what OP wants to prevent.
The doc. of QTextDocument::setHtml() doesn't mention anything specific whether something is used which could be accessed directly (and is even part of the Qt core). Hence, I had a look into source code. I started with QTextDocument::setHtml() on woboq.org and followed the bread crumbs.
Finally, I ended up in qtbase/src/gui/text/qtexthtmlparser.cpp:
QString QTextHtmlParser::parseEntity()
{
const int recover = pos;
int entityLen = 0;
QStringRef entity;
while (pos < len) {
QChar c = txt.at(pos++);
if (c.isSpace() || pos - recover > 9) {
goto error;
}
if (c == QLatin1Char(';'))
break;
++entityLen;
}
if (entityLen) {
entity = QStringRef(&txt, recover, entityLen);
QChar resolved = resolveEntity(entity);
if (!resolved.isNull())
return QString(resolved);
if (entityLen > 1 && entity.at(0) == QLatin1Char('#')) {
entity = entity.mid(1); // removing leading #
int base = 10;
bool ok = false;
if (entity.at(0).toLower() == QLatin1Char('x')) { // hex entity?
entity = entity.mid(1);
base = 16;
}
uint uc = entity.toUInt(&ok, base);
if (ok) {
if (uc >= 0x80 && uc < 0x80 + (sizeof(windowsLatin1ExtendedCharacters)/sizeof(windowsLatin1ExtendedCharacters[0])))
uc = windowsLatin1ExtendedCharacters[uc - 0x80];
QString str;
if (QChar::requiresSurrogates(uc)) {
str += QChar(QChar::highSurrogate(uc));
str += QChar(QChar::lowSurrogate(uc));
} else {
str = QChar(uc);
}
return str;
}
}
}
error:
pos = recover;
return QLatin1String("&");
}
A table of named entities can be found in the same source file:
static const struct QTextHtmlEntity { const char name[9]; quint16 code; } entities[]= {
{ "AElig", 0x00c6 },
{ "AMP", 38 },
...
{ "zwj", 0x200d },
{ "zwnj", 0x200c }
};
Q_STATIC_ASSERT(MAX_ENTITY == sizeof entities / sizeof *entities);
These are bad news for OP:
The API of the QTextHtmlParser is private:
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
and it's part of Qt GUI.
If OP insists to prevent GUI dependencies, the only other chance I see is to duplicate the code (or just to re-implement it from scratch).