I want to convert QString to short.when I try this code
ui->lineEdit->text().toShort();
It works well for text = 20 but it returns "0" for value = 20.5.
but I need value = 20. how can I solve it?
The reason that 0 is returned is because a decimal point is an invalid character for the short data type.
If you want to be able to convert floating-point numbers from QString to integers, you need to convert your text to a float or double first, then use normal rounding/truncation to convert to short.
use that convertion string:
ui->lineEdit->text()->split(".")[0].toShort(0,10);
Related
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).
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().
I am trying to insert a special unicode character (0xFD3F) into a QString.
I tried to create QChar(0xFD3F) but when outputting this char and viewing it in a hex editor it shows 0x3F3F.
I couldn't also find a function in QString to insert a character by its hex or decimal representation.
Use QString::fromWCharArray like this:
QString::fromWCharArray(L"Hello \uFD3F Good bye")
Use QString::fromUtf8 like this:
QString::fromUtf8("Hello \uFD3F Good bye")
How can I convert c(mpg,cyl,disp,hp,drat,wt) to c("mpg","cyl","disp","hp","drat","wt")?
I need to add extra double quotes to each element in the vector
Try either
paste(quote(c(mpg,cyl,disp,hp,drat,wt)))[-1]
Or
as.character(substitute(c(mpg,cyl,disp,hp,drat,wt)))[-1]
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.