QMap iteration crash

nullstellensatz

I am using Qt 5.5 on Windows 8.1. When I run the code below, the application is able to get through one iteration, but crashes on the second one. 100% reproducible. (Copy/paste it into a Qt Creator instance and test; it might work for you).

#include <QCoreApplication>
#include <QDebug>
#include <utility>

using std::pair;

int main(int argc, char *argv[]) {
    QCoreApplication a(argc, argv);
    QMap<QString, pair<QString, QString> > table_def = {
        {"alpha", {"INTEGER", "PRIMARY KEY"}},
        {"beta", {"VARCHAR", ""}},
        {"gamma", {"VARCHAR", ""}},
        {"delta", {"REAL", "DEFAULT 0"}},
        {"epsilon", {"INTEGER", ""}},
        {"zeta", {"INTEGER", ""}},
        {"eta", {"INTEGER", ""}},
        {"theta", {"INTEGER", ""}},
        {"iota", {"VARCHAR", ""}},
        {"kappa", {"INTEGER", "DEFAULT 0"}},
        {"lambda", {"INTEGER", "DEFAULT 0"}}
    };

    QMapIterator<QString, pair<QString, QString> > it(table_def);
    while (it.hasNext()) {
      it.next();
      const QString& col_name = it.key();
      qDebug() << col_name;
      const QString& col_type = it.value().first;
      qDebug() << col_type;
      const QString& extra_def = it.value().second;
      qDebug() << extra_def;
    }
    return a.exec();
}

My Visual Studio debugger says: Unhandled exception at 0x000000006904E394 (Qt5Cored.dll) in helloqt.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

If it is of any relevance, I added DEFINES += Q_COMPILER_INITIALIZER_LISTS in my project file to enable initialization of QContainers with initializer lists. Also, if I replace the STL pair with QPair, the application crashes at the first iteration.

I don't see anything wrong with this code. What could be happening?

mrjj

@nullstellensatz said:

qt 5.4.1 on win 7.
No crash with your code.
also added DEFINES += Q_COMPILER_INITIALIZER_LISTS

for test, if you change all "" (empty) to something , does it still crash ?
Just a thought since you say it crash on second. (first "")

Code looks perfectly valid to me.

nullstellensatz

The first entry to be printed is actually "theta" (since the entries are not ordered by key), which has an empty string as the second value.

Chris Kawa

Which version and update of VS are you using?
Initializer lists were infested with subtle but horrid bugs prior to VS2013 Update 3 and are not entirely standards conforming even in Update 4, although the above seems to compile and run fine with Qt5.5 in VS2013 Update 4 (the extra define seems not needed anymore?).

nullstellensatz

@Chris-Kawa The last time I updated Visual Studio was sometime in 2014. After getting the most recent version of Visual Studio this probelm went away.

Chris Kawa

Great.

Btw. you can check which update you're running by going to Help->About Microsoft Visual Studio.
For example the latest update reads
Microsoft Visual Studio 2013
Version 12.0.31101.00 Update 4

Btw 2. On monday (20.07.2015) VS 2015 comes out, which has greatly improved c++11 standard support.