How to convert int to QString?

Question

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

Answer 1

Use QString::number():

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

Answer 2

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);

Answer 3

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();

Answer 4

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.

Answer 5

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.

Answer 6

A more advanced way other than the answer of Georg Fritzsche:

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

Get the documentation and an example here.

Answer 7

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

Answer 8

Just for completeness, you can use the standard library and do:

QString qstr = QString::fromStdString(std::to_string(42));

Answer 9

QLocale has a handy way of converting numbers.  It's not much more typing than the accepted answer, but is more useful in the case of floats; so I like to do both this way.  Here's for an int:

int i = 42;
QString s = QLocale().toString(i);

and here's for a float:

float f=42.5;
QString s = QLocale().toString(f, 1);

the last argument is the number of decimal places.  You can also insert a char format argument such as 'f' or 'e' for the second parameter. The advantage of this, is if your program is then run in a locale where a comma is used as a decimal "point", it will automatically print it that way.  It's not included in something like <QCoreApplication>, so you'll have to do an #include <QLocale> somewhere, of course.  It really comes into its own in formatting currency strings.

It has the slight performance downside of requiring the creation and deletion of an object during the evaluation, but were performance an issue, you could just allocate it once, and use it repeatedly.

You could write:

QString s = QString::number(42.5, 'f', 1);

but according to the help "Unlike QLocale::toString(), this function does not honor the user's locale settings."