How to convert int to QString?

Question

Is there a QString function which takes an int and outputs it as a QString?

score 721 · Accepted Answer · edited Aug 17 '15 at 07:38

721

Use QString::number():

int i = 42;
QString s = QString::number(i);

edited Aug 17 '15 at 07:38

tomvodi

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answered Jul 09 '10 at 10:33

Georg Fritzsche

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Here's the more interesting question: is there a faster way? I have encountered a problem where this version almost takes more time than the entire processing afterwards... – Zeks Apr 04 '17 at 18:22
1

Then you probably want to work on pre-allocated buffers... but this sounds like a separate question. – Georg Fritzsche Apr 06 '17 at 04:45

score 123 · Answer 2 · edited Apr 07 '16 at 20:10

123

And if you want to put it into string within some text context, forget about + operator. Simply do:

// Qt 5 + C++11
auto i = 13;    
auto printable = QStringLiteral("My magic number is %1. That's all!").arg(i);

// Qt 5
int i = 13;    
QString printable = QStringLiteral("My magic number is %1. That's all!").arg(i);

// Qt 4
int i = 13;    
QString printable = QString::fromLatin1("My magic number is %1. That's all!").arg(i);

edited Apr 07 '16 at 20:10

Kuba hasn't forgotten Monica

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answered Jul 09 '10 at 20:12

Kamil Klimek

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Since you mention the `+` operator, careful around integers, since it might very well work but internally, the `operator+(const QString &s, char c)` implementation is called, and the string wont contain the integer as number but its `QChar::fromAscii(c)` equivalent – x29a Jul 23 '15 at 08:19
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Since you mention the + operator, you can actually do it, but understanding whats happening: QString p = s + QString::number(1); being s a QString works perfectly. So, basically QString + QString is okay, QString + int **bad**. – David Sánchez Aug 12 '15 at 09:25

Gabriel de Grimouard · Answer 3 · 2018-04-18T15:16:23.677

28

Moreover to convert whatever you want, you can use QVariant. For an int to a QString you get:

QVariant(3).toString();

A float to a string or a string to a float:

QVariant(3.2).toString();
QVariant("5.2").toFloat();

edited Apr 18 '18 at 15:16

answered Feb 07 '15 at 10:49

Gabriel de Grimouard

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Call me nuts, but I'd get more use out of the question as "How to convert a number to QString?", this as the main answer for lightweight conversions, and the other answers for special treatments. – mr3 Jul 18 '17 at 23:47

score 17 · Answer 4 · edited Apr 28 '16 at 21:09

Yet another option is to use QTextStream and the << operator in much the same way as you would use cout in C++:

QPoint point(5,1);
QString str;
QTextStream(&str) << "Mouse click: (" << point.x() << ", " << point.y() << ").";

// OUTPUT:
// Mouse click: (5, 1).

Because operator <<() has been overloaded, you can use it for multiple types, not just int. QString::arg() is overloaded, for example arg(int a1, int a2), but there is no arg(int a1, QString a2), so using QTextStream() and operator << is convenient when formatting longer strings with mixed types.

Caution: You might be tempted to use the sprintf() facility to mimic C style printf() statements, but it is recommended to use QTextStream or arg() because they support Unicode strings.

score 15 · Answer 5 · edited Apr 28 '16 at 21:36

15

I always use QString::setNum().

int i = 10;
double d = 10.75;
QString str;
str.setNum(i);
str.setNum(d);

setNum() is overloaded in many ways. See QString class reference.

edited Apr 28 '16 at 21:36

Angie Quijano

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answered Jul 11 '10 at 11:05

Narek

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score 12 · Answer 6 · edited Aug 30 '16 at 14:08

12

In it's simplest form, use the answer of Georg Fritzsche

For a bit advanced, you can use this,

QString QString::arg ( int a, int fieldWidth = 0, int base = 10, const QChar & fillChar = QLatin1Char( ' ' ) ) const

Get the documentation and an example here..

edited Aug 30 '16 at 14:08

mnme

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answered Jul 09 '10 at 10:43

liaK

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Unfortunately, the link to the Nokia site no longer works. – Eliyahu Skoczylas May 22 '16 at 16:35

score 4 · Answer 7 · answered Aug 19 '18 at 17:03

4

If you need locale-aware number formatting, use QLocale::toString instead.

answered Aug 19 '18 at 17:03

André

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score 3 · Answer 8 · answered Apr 12 '16 at 05:06

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Just for completeness, you can use the standard library and do QString qstr = QString::fromStdString(std::to_string(42));

answered Apr 12 '16 at 05:06

Morgan

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How to convert int to QString?

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