Unexpected QList behaviour with nested structures.

Gourmand

Following strustured types defined:

@typedef struct {
const char* str;
const QObject* obj;
} NObj;

typedef struct {
NObj v1;
NObj v2;
} twoPairs;@

then in some class I create private: QList<twoPairs> pairs;

All works fine until I try get values from this list.

I add data using this:

@tmp.v1.str = someptr1;
tmp.v1.obj = someptr2;
tmp.v2.str = someptr3;
tmp.v2.obj = someptr4; // here all is fine, fields are right

pairs << tmp; // unfortunately QtCreator doesn't show pairs content
@

but while doing something like this

@foreach( twoPairs pair, pairs )
{
char* x1 = pair.v1.str; // is fine
QObject x2 = pair.v1.obj; // is fine
char* x3 = pair.v2.str; // ----CORRUPTED!!----
QObject x4 = pair.v2.obj; // is fine
}@

And this appears while any other attempt to get structure from QList. Even in:

@ tmp = pairs.at(0);
char* x1 = tmp.v1.str; // is fine
QObject x2 = tmp.v1.obj; // is fine
char* x3 = tmp.v2.str; // ----CORRUPTED!!----
QObject x4 = tmp.v2.obj; // is fine
@

What is wrong with these structures? Isn't that a bug in QList implementation? Anybody confirm?

koahnig

What makes you believe that this is a QList problem?
It could also be that the memory of the original char * has been released.

Gourmand

released WHERE? in foreach() or at() ?? and it can't be released anywhere because it is statically initialized - it contains pointer to static "string"

of course may be I'm just getting tired... working for 14 hours today... may be...

Uwe Kindler

Your code has a lot of bugs and won't even compile.
@char* x1 = pair.v1.str; // is fine@
No, this is not fine because you assign a const char* to a char* without a const cast.
@QObject x2 = tmp.v1.obj; // is fine@
No, this is even more worse because you assign a QObject pointer to a QObject instance.
From reading your code I'm not surprised that QList shows unexpectet behaviour. But maybe the QList programmer created a serious bug because he was tired after 14 hours of work. ;)

andre

Gourmand, this is the third topic in a short time where you claim very well tested Qt libs have bugs. Perhaps you should mind "this item":http://www.catb.org/~esr/faqs/smart-questions.html#id478549 from the "Smart Questions FAQ":http://www.catb.org/~esr/faqs/smart-questions.html.

Gourmand

bq. Your code has a lot of bugs and won’t even compile.

this was not exactly copy-pasted code, here was just idea, exactly there was my mistake but not in this code, in other place, now all this work fine, sorry

jim_kaiser

@ const QObject* obj; @

You cannot have a const pointer and then assign to it normally. Only in the initializer list of constructor or when defining it. Either

@
const QObject* obj = <some_qobject_pointer>;
@

or

@
struct ABC {

ABC(QObject* obj_param)
: obj(obj_param)
{
}

const QObject*  obj;

};

QObject* myObj = new QObject();
struct ABC a(myObj);
@

Other issues in the code, you don't allocate memory anywhere..
Do this:

@
struct ABC
{
char* str;
}

struct ABC a;
a.str = strdup("your const char* string");
@

strdup duplicates string, allocates memory and returns it.

If you say, it's solved, then could you add [ Solved ] in the title.

Gourmand

bq. You cannot have a const pointer and then assign to it normally.

You can't read? I already told - real code was different. I was after 14 hours of permanent work and entered wrong code here. All my tens of thousands lines work fine.

Anybody can close this thread?

mgran

[quote author="Gourmand" date="1308662520"]You can't read? I already told - real code was different. I was after 14 hours of permanent work and entered wrong code here. All my tens of thousands lines work fine.

Anybody can close this thread?[/quote]

People here are trying to help you Gourmand, so please be nice and watch what you write.

-MariusG
Admin

Gourmand

I already don't need help. When I'll need - I'll ask for it. Sorry. Please close this thread.

giesbert

Gourmand: please be patient. All people here are here because they like Qt and in their free time. If you get rude, you will get no answers. So I suggest, you keep being patient.

EDIT: closed the thread