"this" is 0 in debuger

OpenGL

I'm trying to find an issue in my code that is strange. Everything seems to work, but when I call a method (set_value) of an object of a custom class it crashes.
The code looks like this (with a lot of code cut away)

class MyClass : public QWidget 
{
private:
    QString m_name;
}

void MyClass::set_value(QString key, QString value)
{
    qDebug()<<value;  // debug is added to this line
    qDebug()<<m_name;  // m_key is a member of the class.

In the console window in qtcreator I see the value "value" printed, but it crashes when it tries to print m_name.
I can successfully add

 qDebug()<<m_name;

in the constructor.

When I try to debug, I add a breakpoint in set_value and it shows in the "Local and Expressions" window:
this 0x0

and that can't be good, can it?
Any suggestions on where to start looking for the problem? It seems counter-intuitive to reach the set_value function if "this" would really be null.

mrjj

Hi
Can you show how you use the/a instance of MyClass ?
Maybe you have an out of scope issues as otherwise it sounds odd.

kshegunov

@OpenGL said in "this" is 0 in debuger:

and that can't be good, can it?

It ain't.

Any suggestions on where to start looking for the problem? It seems counter-intuitive to reach the set_value function if "this" would really be null.

Where you call that function with a null pointer - i.e. use the call stack in the debugger and step out of set_value(). There's where you should look for the problem.

OpenGL

I found the issue. I was adding the MyClass objects to a Map with the wrong key.
Hint: never use toInt() without verifying the conversion....