Convert an int to a QString with zero padding (leading zeroes)

Question

I want to "stringify" a number and add zero-padding, like how printf("%05d") would add leading zeros if the number is less than 5 digits.

score 185 · Accepted Answer · edited Jul 10 '20 at 12:14

185

Use this:

QString number = QStringLiteral("%1").arg(yourNumber, 5, 10, QLatin1Char('0'));

5 here corresponds to 5 in printf("%05d"). 10 is the radix, you can put 16 to print the number in hex.

edited Jul 10 '20 at 12:14

Trass3r

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answered Apr 11 '10 at 19:45

chalup

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Thanks. Documentation [here](http://qt-project.org/doc/qt-4.8/qstring.html#arg-10). – migas Mar 18 '14 at 11:02
2

Very useful for creating hex color codes from integer, thanks :) – Michal Aug 21 '15 at 11:07
And why the string argument is `"%1"`? – dhein Jun 08 '16 at 14:05
@Zaibis Because it's the first argument. If there were more, they would be `%2` etc. See http://doc.qt.io/qt-5/qstring.html#arg – Paul Masri-Stone Oct 06 '16 at 18:10
@sashoalm how we can remove the same number of leading zero? ex. My hex was 1f with QString("%1").arg(yourNumber, 5, 10, QChar('0')); it became 001f. now how to do the reverse to get 1f again? thanks for the help in an advance. – Jimit Rupani Feb 15 '18 at 13:53
Correspondent with QByteArray: QByteArray::number(yourNumber, 10).rightJustified(5, '0'); – cleybertandre May 05 '20 at 13:42
There should be a more efficient way to do this. – Trass3r Jul 10 '20 at 12:11

score 45 · Answer 2 · answered Nov 19 '15 at 13:49

45

QString QString::rightJustified ( int width, QChar fill = QLatin1Char( ' ' ), bool truncate = false ) const

int myNumber = 99;
QString result;
result = QString::number(myNumber).rightJustified(5, '0');

result is now 00099

answered Nov 19 '15 at 13:49

Дмитрий Гранин

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thank you, I'm creating a string on the fly using += so the selected solution couldn't be used. – Rudy Barbieri Sep 08 '17 at 10:15
Better but still creates a temporary string :/ – Trass3r Jul 10 '20 at 12:12

score 19 · Answer 3 · edited Oct 22 '14 at 11:09

19

The Short Example:

int myNumber = 9;

//Arg1: the number
//Arg2: how many 0 you want?
//Arg3: The base (10 - decimal, 16 hexadecimal - if you don't understand, choose 10)
//      It seems like only decimal can support negative numbers.
QString number = QString("%1").arg(myNumber, 2, 10, QChar('0')); 

Output will be: 09

edited Oct 22 '14 at 11:09

elcuco

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answered Oct 10 '14 at 23:07

user1767754

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score 5 · Answer 4 · edited Jun 17 '12 at 07:17

5

Try:

QString s = s.sprintf("%08X",yournumber);

EDIT: According to the docs at http://qt-project.org/doc/qt-4.8/qstring.html#sprintf:

Warning: We do not recommend using QString::sprintf() in new Qt code. Instead, consider using QTextStream or arg(), both of which support Unicode strings seamlessly and are type-safe. Here's an example that uses QTextStream:

QString result;
QTextStream(&result) << "pi = " << 3.14;
// result == "pi = 3.14"

Read the other docs for features missing from this method.

edited Jun 17 '12 at 07:17

elcuco

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answered Sep 09 '11 at 15:08

Isaac

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nice, not marking as the best fix, as the currently marked answer is more flexible. But nice to know! (upvoting) – elcuco Sep 12 '11 at 19:37

score -1 · Answer 5 · answered Aug 18 '15 at 21:47

-1

I use a technique since VB 5

QString theStr=QString("0000%1").arg(theNumber).right(4);

answered Aug 18 '15 at 21:47

Ramao Balta

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A lot of memcpy() and a log of wasted memory/cpu. If you are using Qt/C++ you want performance (that said, I saw this trick using in JS, and it's a good hack on that platform). – elcuco Aug 19 '15 at 14:02
4

Don't give up!! – Lennart Rolland Feb 13 '17 at 18:47

score -2 · Answer 6 · answered Apr 11 '10 at 20:17

-2

I was trying this (which does work, but cumbersome).

QString s;
s.setNum(n,base);
s = s.toUpper();
presision -= s.length();
while(presision>0){
    s.prepend('0');
    presision--;
}

answered Apr 11 '10 at 20:17

elcuco

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Convert an int to a QString with zero padding (leading zeroes)

6 Answers6

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