How to print string literal and QString with qDebug?

Question

Is there any easy way to get the following work? I mean is there any helper class in Qt which prepares the string for qDebug?

QString s = "value";
qDebug("abc" + s + "def");

Solution 1

No really easy way I am aware of. You can do:

QByteArray s = "value";
qDebug("abc" + s + "def");

or

QString s = "value";
qDebug("abc" + s.toLatin1() + "def");

Solution 2

You can use the following:

qDebug().nospace() << "abc" << qPrintable(s) << "def";

The nospace() is to avoid printing out spaces after every argument (which is default for qDebug()).

Solution 3

According to Qt Core 5.6 documentation you should use qUtf8Printable() from <QtGlobal> header to print QString with qDebug.

You should do as follows:

QString s = "some text";
qDebug("%s", qUtf8Printable(s));

or shorter:

QString s = "some text";
qDebug(qUtf8Printable(s));

See:

• http://doc.qt.io/qt-5/qtglobal.html#qPrintable

• http://doc.qt.io/qt-5/qtglobal.html#qUtf8Printable

Solution 4

Option 1: Use qDebug's default mode of a C-string format and variable argument list (like printf):

qDebug("abc%sdef", s.toLatin1().constData());

Option 2: Use the C++ version with overloaded << operator:

#include <QtDebug>
qDebug().nospace() << "abc" << qPrintable(s) << "def";

Reference: https://qt-project.org/doc/qt-5-snapshot/qtglobal.html#qDebug

Solution 5

Just rewrite your code like this:

QString s = "value";
qDebug() << "abc" << s << "def";

View more solutions

Comments

[Greenflow]

That's not the same. Your code returns 'abc "value" def'. His code 'abcvaluedef'. Different use case.

[Daniël Sonck]

It's recommended to use qUtf8Printable over qPrintable according to the docs, because qDebug() (and friends) expect UTF-8 which may not always be what toLocal8Bits() (which is what qPrintable calls) returns

[kimbaudi]

this should really be the new accepted answer. I would definitely prefer to use qUtf8Printable and qPrintable over .toLatin1().constData() and C++ << operator.