How to convert int to QString?

Question

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

Solution 1

Use QString::number():

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

Solution 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);

Solution 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();

Solution 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.

Solution 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.

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Comments

[x29a]

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

[David Sánchez]

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.

[Eliyahu Skoczylas]

Unfortunately, the link to the Nokia site no longer works.

[Zeks]

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...

[Georg Fritzsche]

Then you probably want to work on pre-allocated buffers... but this sounds like a separate question.

[mr3]

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.