Segmentation fault when getting QString

Question

Strange problem, already looked into with several colleagues... Using Qt Creator and Qt 4.8.5

define an object
set a number of values with setters
request values with a getters
result: getting an int no problem, all other values give segmentation fault
but with breakpoint in debugger the values are correctly shown, so they are in the object!

same code worked before, problem "just appeared". Compiler issue?

private:
    int id;
    QString name;

public;
   int getId() { return this->id; } // OK
   void setId(int id) { this->id = id; } 

   QString getName() { return this->name; } // SIGSEGV
   void setName(QString name) { this->name = name; }

Any ideas? Same issue known?

UPDATE

Changed code to this, based on comments, still same issue

    private:
        int id;
        QString name;

    public;
       int getId() { return id; } // OK
       void setId(int setTo) { id = setTo; } 

       QString getName() { return name; } // SIGSEGV
       void setName(QString setTo) { name = setTo; }

Did you may recently update Qt libs? May wrong version of library is being used. Try removing (renaming) any probable collision libraries temporarely. — Sebastian Lange, Feb 25 '15 at 09:22
`this->name = name;`? Maybe compiler misunderstood what you intended to do there, because `name`, `this->name` and local variable `name` collision? — vahancho, Feb 25 '15 at 09:48
@vahancho: tried changing that before already without luck... — Frank, Feb 25 '15 at 09:54
Try commenting `this->name = name;` and see if problem persists. Also, is `this` deleted before getJourneyName() gets called? — fxam, Feb 25 '15 at 09:59
@Frank, the same for `this->id = id;`. Try to comment it as well as `this->name = name`. — vahancho, Feb 25 '15 at 10:01
same issue ... I end up here as error: file qstirng.h: { Q_ASSERT(&other != this); d->ref.ref(); } — Frank, Feb 25 '15 at 10:29
It could be your object got deleted before getName() is called. Example: `Bar *b = new Bar; b->setName("Katie"); delete b; qDebug() << b->getName();` — fxam, Feb 25 '15 at 11:02
To check the object deletion sequence, output something in destructor and in getName() and see the order of output. Example: `~Bar() { qDebug() << "dtor()"; } QString getName() { qDebug() << "getName()"; return name; }`. If the output is dtor() then getName(), then the object is used after deleted. Or you can just put breakpoints in dtor and getName() and see who gets called first. — fxam, Feb 25 '15 at 11:11
What about commenting code inside setName? `void setName(QString setTo) { //name = setTo; }` Does that segfault happen too? — fxam, Feb 25 '15 at 11:28
@fxam, yes still happens. when breaking at the getName line, I can see the value is set to the name variable. Fu**** QT just doens't want to return it ;-) — Frank, Feb 25 '15 at 12:08
Is your class QObject-derived? Does it have non-default ctor? — Matt, Feb 25 '15 at 13:20
I guess you need to provide a [minimal reproducible code](http://sscce.org/) here :) — fxam, Feb 25 '15 at 13:43
could try separating the implementation out of the header and see if the same error occurs? — AngryDuck, Feb 25 '15 at 17:19

score 2 · Answer 1 · answered Apr 09 '18 at 12:06

I was facing similar issue. Although I could not find the root cause of this issue, I have another observation. If we define the getter functions outside the class declaration using scope resolution operator the code works.

QString MyClass::GetX(void) {
    return mX;
}

QString MyClass::GetY(void) {
    return mY;
}

class MyClass
{
public:
    MyClass(){}

    /* Functions for setting mX and mY strings. */

    QString GetX(void);

    QString GetY(void);

    isDataAvailable()
    {
        return mAvailable;
    }

private:
    bool mAvailable;
    QString mX;
    QString mY;
};

As I understand, in C++, if we define a function within class declaration, by default it is inline... so the issue could be something related with inlining of the functions.

I think [AngryDuck](https://stackoverflow.com/users/1110338/angryduck) suggested same solution... For me it works. Saw the comment later. — AVD, Apr 09 '18 at 12:09

score 1 · Accepted Answer · answered Feb 26 '15 at 08:05

thinking further about the way objects are created in memory, I thought that a QString maybe doesn't reserve fixed number of bytes, which could be the cause of this strange behavior and guess what, a dummy change solved my problem...

This feels like a really "dirty" solution, but at least I can go on with my work ;-) But any idea's on the root cause would really be appreciated! Thanks already for all the valuable comments!!!

private:
    QString name; // FIRST DEFINE QSTRING
    int id; // THEN DEFINE INT

public;
   int getId() { return id; } // OK
   void setId(int setTo) { id = setTo; } 

   QString getName() { return name; } // OK
   void setName(QString setTo) { name = setTo; }

Segmentation fault when getting QString

UPDATE

2 Answers2