Adding items to a list

Monkey666

Hi guys, I am an advanced C# coder who is trying to transition over to real coding in C++ but getting stuck on some hurdles, which normally would be easy in C#.

Here is what I am trying to do:

@
MyForm::MyForm(QWidget *parent) :
QDialog(parent),
ui(new Ui::MyForm)
{
ui->setupUi(this);
ui->myList->clear();
if (createProcessList())
{
list<ProcInfo>::const_iterator p;
for (p=procList.begin();p!=procList.end(); ++p)
{
ui->myList->addItems(*p);
}
}
}
@

In C# this would work by using the base string To.String() to name the items when adding to a list, however here it seems alot different and I cannot figure it out.

Any help would be appreciated. Thanks.

Edit: Forgot to mention, procList is a list of processes already generated elsewhere in the application:

@
list<ProcInfo> procList;
@

loladiro

Well if there's no implicit conversion from your ProcInfo class to QString, you'd have to call the appropriate method yourself e.g.
@
ui->myList->addItem((*p).name());
@
Also, in your snippet you use addItems, while (I guess), it should be addItem.

Monkey666

Hi, I seem to get a compile error:

error: 'const class ProcInfo' has no member named 'name'.

I'm guessing I have to create the method, in which case how would one create a QString method inside the ProcInfo class?

dangelog

Of course! Adapt that snippet to what you're actually doing!

What's your ui->myList? And what's a ProcInfo?

Monkey666

myList is a listbox widget on the app, and ProcInfo:

@class ProcInfo
{
public:
HANDLE Proc;
DWORD Base;
int ID;
};@

dangelog

And exactly what do you want to add to that list? Because there's nothing resembling a string inside your ProcInfo class...

Monkey666

I want to add each ProcInfo contained in the list to the listbox, but from your repsonse I am guessing you can't add custom class items to a listbox the same way you can in C#.

loladiro

even in C# you need to have a ToString method. How would C++ what you actually want to print. That being said. What do you want to print? The id? In that case you could have an implicit cast to QString like:
@
class ProcInfo
{
public:
//code
operator QString() const
{
return QString::number(id);
}
};
@
or you could call QString::number in the loop instead of adding an implicit cast function:
@
ui->myList->addItem(QString::number((*p).id));
@

Monkey666

[quote author="loladiro" date="1312196973"]even in C# you need to have a ToString method. How would C++ what you actually want to print. [/quote]

No you don't in C#, because when you create a class it automatically has a base ToString() method which is automatically used in certain controls like listboxes without being called (although the string would be simply the class name unless you override the method) I assumed C++ would be no different but clearly it is.

Thanks for the help.

Monkey666

How would I use your operator QString() const method? I can tell I have a long way to go int he conversion from C# to C++ :(

loladiro

Sorry, I forgot about that in C# (I have only once looked into it and that very briefly). However, if you consider your issue solved, pleas add [Solved] in front of the thread title (by editing the first post).

Monkey666

I can't work out actually how to use your operator QString() const.

loladiro

The posts must have crossed in the air ;). The QString() const method is an "explicit coversion operator":http://msdn.microsoft.com/en-us/library/ts48df3y(v=vs.80).aspx . However, be aware that there are also many bugs that may follow from the misuse of this laguage feature.

EDIT: you can use it just like ou would in C# (i.e. without doing anything special)

Monkey666

That's what I thought but get compiler error:

error: no matching function for call to 'QListWidget::addItem(const ProcInfo&)'

Monkey666

Actually there are more compile errors I should have mentioned which are most likely causing this:

error: no match for 'operator=' in 'p = procList.std::list<_Tp, _Alloc>::begin with _Tp = int, _Alloc = std::allocator<int>'

loladiro

Sorry but I can't reproduce. This all works:
@
class ProcInfo
{
public:
int id;
ProcInfo() : id(1234)
{}
operator QString() const
{
return QString::number(id);
}
};

void print(QString print)
{
qDebug() << print;
}

int main(int argc, char *argv[])
{
QApplication a(argc, argv);

QList< ProcInfo > list1;
list1 << ProcInfo();
QList< ProcInfo >::const_iterator i = list1.begin();

std::list< ProcInfo > list2;
list2.push_back(ProcInfo());

std::list< ProcInfo >::const_iterator i2 = list2.begin();

print(*i2);

print (*(i));

QListWidget widget;
widget.addItem(*i);

std::list< ProcInfo >::const_iterator p = list2.begin();

for (p=list2.begin();p!=list2.end(); ++p)
{
    widget.addItem(*p);
}

widget.show();

const ProcInfo p2;
print(p2);

return a.exec(&#41;;

}
@

Monkey666

Ok I've managed to get rid of all compile errors except this one:

error: expected type-specifier before 'QString'

And the error points to the operator:

@
class ProcInfo
{
public:
HANDLE Proc;
DWORD Base;
int ID;
operator QString() const
{
return QString::number(ID);
}
};@

loladiro

did you #include <QString>?

Monkey666

That fixed that but now I have another problem /sigh.

I have declared std::list<ProcInfo> procList; inside a header file, and that header file is included in the main cpp file which I am doing this all in, however I get error:

error: multiple definition of `procList'

There is definitely only 1 definition and it's inside the h file so I'm a little confused, maybe c++ isn't for me :(

loladiro

There's not much we can do without seeing the header file ...