Qt Test QVERIFY2() string and int concatenation

Question

Sorry for the bad title, I have no idea how to title this question. Please edit and make it better.

I am writing a test using the Qt test framework, and I'm trying to write some useful output to be used by the QVERIFY2() macro. All of the following statements have failed to compile with roughly the same error message:

QVERIFY2( spy.count() == 1, "Emitted signal pathChanged() was emitted " + spy.count() + " times instead of 1 time" );
QVERIFY2( spy.count() == 1, QString( "Emitted signal pathChanged() was emitted " ) + QString( spy.count() ) + QString( " times instead of 1 time" ) );
QVERIFY2( spy.count() == 1, "Emitted signal pathChanged() was emitted " + QString( spy.count() ) + " times instead of 1 time" );

The error message for the last attempt was:

PathTester.cxx: In member function ‘void PathTester::testReservePath()’:
PathTester.cxx:241:128: error: cannot convert ‘QString’ to ‘const char*’ for argument ‘3’ to ‘bool QTest::qVerify(bool, const char*, const char*, const char*, int)’
PathTester.cxx:241:243: error: cannot convert ‘QString’ to ‘const char*’ for argument ‘3’ to ‘bool QTest::qVerify(bool, const char*, const char*, const char*, int)’

What am I doing wrong? How can I write that correctly?

Answer 1

Use QVERIFY2(condition, qPrintable(...)) when using a QString.

The second argument must be a const char *. In all of your cases you're creating a QString instead -- which is indeed very convenient because it allows you to use + for concatenation, or QString::arg(), etc; you need a conversion to char *, which is not implicit, and that's what qPrintable() does.

_{To elaborate: qPrintable(string) is a shorthand for string.toLocal8Bit().constData(). Qt 5.4 will also introduce qUtf8Printable(string) which is the equivalent of string.toUtf8().constData().}

Addendum: apart from the technicality of what to pass to QVERIFY2, why aren't you using QCOMPARE(spy.count(), 1)? In case of failure it will emit the expected value and the actual value.

Answer 2

I'd like to add my 5 cents. While you actually may use QCOMPARE in your specific case as @peppe suggested, sometimes you may need to provide a more detailed message. That the case for QVERIFY2. The best way for formatting message in this case that I know is exploitation of QString::arg() method. For example in you case you could write:

QVERIFY2 (
    spy.count() == 1, 
    qPrintable (
        QString ("Emitted signal pathChanged() was emitted %1 times instead of %2 time(s)")
        .arg (spy.count())
        .arg (1)));

This way you get a more readable code and may change both actual count and expected count expressions.