Solved Pretty C++ general question (using Qt)

[U7Development]

Hi mates.. first of all, my apologies if this does not belong to Qt Development itself, i guess is somehow related...

I have many QLabels on my form, i decided to use a standard vector to contain them, so i can iterate the vector to configure my QLabels shortly. For ranged detects the QLabel function members, but standard iterator does not, why?

for (std::vector<QLabel*>::iterator ite = vQLabels.begin(); ite != vQLabels.end(); ++ite) { 
        *ite = new QLabel;       // <--- this is OK
        *ite->setStyleSheet(C_STYLESHEET_FIELD);     // <---- Error no member named setStyleSheet in __gnu_cxx
}

it is supposed that ite is the iterator pointing to QLabel object isn't ?

But this works....

for (auto& v : vQLabels){
      v->setStyleSheet(C_STYLESHEET_FIELD);     // <----- correct
}

Any ideas?.
Thanks so much.

[JonB]

@U7Development said in Pretty C++ general question (using Qt):

*it->setStyleSheet(C_STYLESHEET_FIELD); // <---- Error no member named setStyleSheet in __gnu_cxx

Guess (I like making these ;) ): what's the precedence of that leading *, compared to ->? Isn't it supposed to be:

(*it)->setStyleSheet(C_STYLESHEET_FIELD);

[JonB]

@U7Development said in Pretty C++ general question (using Qt):

*it->setStyleSheet(C_STYLESHEET_FIELD); // <---- Error no member named setStyleSheet in __gnu_cxx

Guess (I like making these ;) ): what's the precedence of that leading *, compared to ->? Isn't it supposed to be:

(*it)->setStyleSheet(C_STYLESHEET_FIELD);

[U7Development]

ohh you are right that works.. thanks.

what i did not get is ite is supposed to be a pointer poiting to the QLabel pointer itself .. so theoretically if I use -> I could access to member functions too... seems weird isn't ?.

for (std::vector<QLabel*>::iterator ite = vQLabels.begin(); ite != vQLabels.end(); ++ite) { 
        *ite = new QLabel;     
        QLabel*& lab = *ite;
        lab->setStyleSheet(C_STYLESHEET_FIELD);     // <--- this is OK
}

Is the (*) a conventional prefix to use while containing pointers only ?
Thanks again..

[J.Hilk]

@U7Development said in Pretty C++ general question (using Qt):

Is the (*) a conventional prefix to use while containing pointers only ?
Thanks again..

the * has generally speaking 2 roles:

• When used in a declaration (e.g. QLabel *label), it "creates" a pointer variable
• When not used in a declaration, it is a dereference operator

You can read it as "the value pointed to by"
see here for more information

---

edit:

just as an FYI you could also write
(*(*it)).setStyleSheet(C_STYLESHEET_FIELD);
See here for more information

[JonB]

@J-Hilk said in Pretty C++ general question (using Qt):

the * has generally speaking 2 roles:

So not multiplication then? ;-)

[Pl45m4]

@JonB

Multiplication?!
I thought asterisk is a wildcard character in C++? :o

QString a = "DoNotBelieve";
QString b = "WhatImWritingHere";

QString aa = "Seriously.Just.Dont";
QString bb = "Seriously.Just.Dont";

if ( *a == *b)
{
      qDebug() << "true, because aa = bb";
}

EDIT:

It hurts even MY eyes :D

[J.Hilk]

@JonB what is multiplication, but a chain of addition? 😎

@Pl45m4
does this compile for you? What compiler?