How to deal with “%1” in the argument of QString::arg()?

Question

Everybody loves

QString("Put something here %1 and here %2")
    .arg(replacement1)
    .arg(replacement2);

but things get itchy as soon as you have the faintest chance that replacement1 actually contains %1 or even %2 anywhere. Then, the second QString::arg() will replace only the re-introduced %1 or both %2 occurrences. Anyway, you won't get the literal "%1" that you probably intended.

Is there any standard trick to overcome this?

If you need an example to play with, take this

#include <QCoreApplication>
#include <QDebug>

int main()
{
    qDebug() << QString("%1-%2").arg("%1").arg("foo");
    return 0;
}

This will output

"foo-%2"

instead of

"%1-foo"

as might be expected (not).

    qDebug() << QString("%1-%2").arg("%2").arg("foo");

gives

"foo-foo"

and

    qDebug() << QString("%1-%2").arg("%3").arg("foo");

gives

"%3-foo"

Answer 1

See the Qt docs about QString::arg():

QString str;
str = "%1 %2";
str.arg("%1f", "Hello"); // returns "%1f Hello"

Answer 2

Note that the arg() overload for multiple arguments only takes QString. In case not all the arguments are QStrings, you could change the order of the placeholders in the format string:

QString("1%1 2%2 3%3 4%4").arg(int1).arg(string2).arg(string3).arg(int4);

becomes

QString("1%1 2%3 3%4 4%2").arg(int1).arg(int4).arg(string2, string3);

That way, everything that is not a string is replaced first, and then all the strings are replaced at the same time.

Answer 3

You should try using

QString("%1-%2").arg("%2","foo");