Qt - QString Numerical Format String (cformat), Options? - qt

I have user-provided format string (e.g. "%.2f") and a QVariant type that I am attempting to combine to output into a (formatted) string.
I had gone down the path of using QString::asprintf(const char *cformat, ...) to achieve this, where I would supply the appropriate converted data type, like this:
QString result_str = QString::asprintf(disp_fmt.toUtf8(),variant_type.toUInt());
This works fine for the most part, especially when I have a floating point as the input. However, if my format string in this particular integer (.toUInt()) conversion case includes decimal formatting (e.g. "%.2f"), then I get a constant result of "0.00". This caught me by surprise as I expected to instead just get ".00" tacked onto the integer, as I have seen in other languages like Perl.
What am I missing here? Also, I know asprintf() was added fairly recently and the documentation already now advises to use QTextStream or arg() instead. I don't believe this to be an option, however, for me to use this style of format string. Thanks.

The format string is expecting a double, but you're providing an int. It works if you provide an actual double, like this:
QString result_str = QString::asprintf(disp_fmt.toUtf8(),variant_type.toDouble());
Also note, this behavior is identical to how the standard C library functions work (std::sprintf, etc).

Related

How to Know The Initial Data type is UTF-8 or UTF-16 in sqlite?

In this, the function sqlite3_column_type can tell me whether the initial data type of the result is text or not, but it will not tell whether it is UTF-8 or UTF-16. Is there a way to know that?
Thanks
If you have a brand new empty database, before any tables are created, you can set the internal encoding used for Unicode text with the encoding pragma, and later use it to see the encoding being used (It defaults to UTF-8).
When storing or retrieving TEXT values, sqlite will automatically convert if needed between UTF-8 and UTF-16, so it doesn't matter too much which one is being used internally unless you're trying to get every last tiny bit of performance out of it.
In the link you provided it says explicitely:
const unsigned char sqlite3_column_text(sqlite3_stmt, int iCol);
const void sqlite3_column_text16(sqlite3_stmt, int iCol);
sqlite3_column_text → UTF-8 TEXT result sqlite3_column_text16 → UTF-16
TEXT result
These routines return information about a single column of the current
result row of a query. In every case the first argument is a pointer
to the prepared statement that is being evaluated (the sqlite3_stmt*
that was returned from sqlite3_prepare_v2() or one of its variants)
and the second argument is the index of the column for which
information should be returned. The leftmost column of the result set
has the index 0. The number of columns in the result can be determined
using sqlite3_column_count().

How do I concatenate strings in arduino?

sorry I am a bit rusty here, how do I concatenate these 2 outputs?
display.println(timeinfo->tm_hour);
display.println(timeinfo->tm_min);
If you just want them to appear in the output one after another on the same line then use print instead of println for the first one. Println adds a newline to the end of the output and print doesn't. It's always good to look stuff like that up before using a function.
If you really want them put together into one string then you will have to show where those strings are coming from. If they are String class objects you can just use + to put them together. If they are proper c-style strings then you will need to use strcat.
How are defining them?
If you have initialized as arrays of characters:
Example: char exampleCString[50] = "This is a C string";
Then you can use strcat() function in C:
strcat(str1,str2);
Note: Make sure "str1" buffer is big enough, because the result goes there.
If on the other hand, you have initialized your strings as objects of String class:
Example: String exampleJavaString="This is a Java String example"
Then just use the + operator to add them:
str1=str1+str2:

Preserve non-ascii characters between std::string and QString

In my program the user can either provide a filename on the command line or using a QFileDialog. In the first case, I have a char* without any encoding information, in the second I have a QString.
To store the filename for later use (Recent Files), I need it as a QString. But to open the file with std::ifstream, I need a std::string.
Now the fun starts. I can do:
filename = QString::fromLocal8Bit(argv[1]);
later on, I can do:
std::string fn = filename.toLocal8Bit().constData();
This works for most characters, but not all. For example, the word Раи́са will look the same after going through this conversion, but, in fact, have different characters.
So while I can have a Раи́са.txt, and it will display Раи́са.txt, it will not find the file in the filesystem. Most letters work, but и́ doesnt.
(Note that it does work correctly when the file was chosen in the QFileDialog. It does not when it originated from the command line.)
Is there any better way to preserve the filename? Right now I obtain it in whatever native encoding, and can pass-on in the same encoding, without knowing it. At least so I thought.
'и́' is not an ASCII character, that is to say it has no 8-bit representation. How it is represented in argv[1] then is OS dependent. But it's not getting represented in just one char.
The fromLocal8bit uses the same QTextCodec::codecForLocale as toLocal8bit. And as you say your std::string will hold "Раи́са.txt" so that's not the problem.
Depending on how your OS defined std::ifstream though std::ifstream may expect each char to be it's own char and not go through the OS's translation. I expect that you are on Windows since you are seeing this problm. In which case you should use the std::wstring implementation of std::fstream which is Microsoft specific: http://msdn.microsoft.com/en-us/library/4dx08bh4.aspx
You can get a std::wstring from QString by using: toStdWString
See here for more info: fstream::open() Unicode or Non-Ascii characters don't work (with std::ios::out) on Windows
EDIT:
A good cross-platform option for projects with access to it is Boost::Filesystem. ypnos Mentions File-Streams as specifically pertinent.

Retrieve Unicode code points > U+FFFF from QChar

I have an application that is supposed to deal with all kinds of characters and at some point display information about them. I use Qt and its inherent Unicode support in QChar, QString etc.
Now I need the code point of a QChar in order to look up some data in http://unicode.org/Public/UNIDATA/UnicodeData.txt, but QChar's unicode() method only returns a ushort (unsigned short), which usually is a number from 0 to 65535 (or 0xFFFF). There are characters with code points > 0xFFFF, so how do I get these? Is there some trick I am missing or is this currently not supported by Qt/QChar?
Each QChar is a UTF-16 value, not a complete Unicode codepoint. Therefore, non-BMP characters consist of two QChar surrogate pairs.
The solution appears to lay in code that is documented but not seen much on the Web. You can get the utf-8 value in decimal form. You then apply to determine if a single QChar is large enough. In this case it is not. Then you need to create two QChar's.
uint32_t cp = 155222; // a 4-byte Japanese character
QString str;
if(Qchar::requiresSurrogate(cp))
{
QChar charArray[2];
charArray[0] = QChar::highSurrogate(cp);
charArray[1] = QChar::lowSurrogate(cp);
str = QString(charArray, 2);
}
The resulting QString will contain the correct information to display your supplemental utf-8 character.
Unicode characters beyond U+FFFF in Qt
QChar itself only supports Unicode characters up to U+FFFF.
QString supports Unicode characters beyond U+FFFF by concatenating two QChars (that is, by using UTF-16 encoding). However, the QString API doesn't help you much if you need to process characters beyond U+FFFF. As an example, a QString instance which contains the single Unicode character U+131F6 will return a size of 2, not 1.
I've opened QTBUG-18868 about this problem back in 2011, but after more than three years (!) of discussion, it was finally closed as "out of scope" without any resolution.
Solution
You can, however, download and use these Unicode Qt string wrapper classes which have been attached to the Qt bug report. Licensed under the LGPL.
This download contains the wrapper classes QUtfString, QUtfChar, QUtfRegExp and QUtfStringList which supplement the existing Qt classes and allow you to do things like this:
QUtfString str;
str.append(0x1307C); // Some Unicode character beyond U+FFFF
Q_ASSERT(str.size() == 1);
Q_ASSERT(str[0] == 0x1307C);
str += 'a';
Q_ASSERT(str.size() == 2);
Q_ASSERT(str[1] == 'a');
Q_ASSERT(str.indexOf('a') == 1);
For further details about the implementation, usage and runtime complexity please see the API documentation included within the download.

Does QString::fromUtf8 automatically reverse a Hebrew string?

I am having a problem where a Hebrew string is being displayed in reverse. I use QTableWidget to display some info, and here the string appears correctly using:
CString hebrewStr; hebrewStr.ToUTF8();
QString s = QString::fromUtf8( hebrewStr );
In another part of my program this same string is displayed on the screen, but not using QT, and this is what is being shown in reverse:
CString hebrewStr;
hebrewStr.ToUTF8();
I have debugged and hebrewStr.ToUTF8() in both cases produces the exact same unicode string, but the string is only displayed correctly in the QTableWidget. So I am wondering if Qt automatically reverses a given Hebrew string (since it is a rigth-to-left language). Thanks!
Yes, in this case QString generate the full unicode wchar_t from the UTF-8 encoded string. If you would like to do similar thing in MFC, you should use CStringW and decode the string.
Use MultiByteToWideChar for UTF8 to CStringW conversion.
Connected question in StackOverflow.

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