CODEWITHSUNDEEP
c++qtunicodeascii
adnan kamili
adnan kamili

Reputation: 9455

how to display extended ascii character in QTextEdit

All the ASCII codes greater than 127 are replaced by Diamond? symbol. How can I display those characters. I have an unsigned char buffer[1024] which contains values from 0 to 256.

Upvotes: 0

Views: 3493

Answers (2)

Dan
Dan

Reputation: 1861

This is a rabbit hole with no end. Qt does not fully support printing ascii > 127 as it is not well defined. The current method is to use "fromLocal8bit()" which will take a char array and transform it into the "right" Unicode string (the only thing Qt supports printing).

QTextCodec::setCodecForLocale can be used to identify the character set you wish to transform from. Many codecs are supported, but for some reason IBM437 (the character set used by IBM PCs in the US for decades) is not supported, where several other codecs used by Europe, etc. are. Probably some characters in IBM437 were never assigned proper code points in Unicode, so transforming it isn't possible?

What's frustrating is that there are fonts with all 256 ascii code points, but it is simply not possible to display these in Qt as they only work with Unicode strings. There are a handful of glyphs they don't support, and it seems to grow with newer versions of Qt. Currently I know of 9, 10, 12, 13, and 173. Some of these are for obvious reasons (usually you don't want to print a carriage return glyph, though it did exist in DOS), but others used to work in Qt and now do not.

In my application, I resorted to creating a new font that has copies of the unprintable glyphs in higher unicode codepoints, and translate them before printing them on the screen. It's quite silly but Qt gave up on ascii many years ago, so it's the best option I could find.

Upvotes: 2

Josh
Josh

Reputation: 760

Use the QString class's fromAscii() method. By default this will treat Ascii chars above 128 as Latin-1 chars. To change this behavior use QTextCodec::setCodecForCStrings method to set the correct codec for your usage.

I believe QT5 may have taken out the setCodecForCStrings method.

EDIT: Adnan supplied the QT5 alternative to setCodecForCStrings method, adding to answer for completeness.

Qt5 alternative for setCodecForCStrings is QTextCodec::setCodecForLocale(QTextCodec::codecForName("UTF-8"));

Upvotes: 4

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