How do I declare a object for use with this function

Question

I have a function which is declared as:

bool getIndex(const QString itemUid, QModelIndex& index /*out*/);

how do I declare an object to pass in as index?

I have tried:

QModelIndex *modelIndex;
getIndex(auid, modelIndex  );

with and without the "*", but I get compile errors.

The compilation error is:

no matching function for call to TreeModel::getIndex(QString, QModelIndex*&)

possible duplicate of [C++: Argument Passing "passed by reference"](http://stackoverflow.com/questions/19827119/c-argument-passing-passed-by-reference) — NathanOliver, Jun 26 '15 at 13:21
@101010 He said he tried it with and without the "*", which I assume refers that exact answer. — Sam Estep, Jun 26 '15 at 13:23
It's hard to believe that *without* "*" gave you compilation errors. What exactly were the errors? — molbdnilo, Jun 26 '15 at 13:23
Your error function signature does not match the function signature you posted. Please edit your question to contain an [SSCCE](http://sscce.org) — NathanOliver, Jun 26 '15 at 13:30
OK - my mistake, without the "*" works. There was an error in the first parameter, too. Thanks for your help. { red faced } — Michael Vincent, Jun 26 '15 at 13:32

score 1 · Accepted Answer · answered Jun 26 '15 at 13:41

Compiling without the * shouldn't give you errors (assuming you are not doing something like QModelIndex *modelIndex();).

Another way to solve your problem would be to declare your function like so :

bool getIndex(const QString itemUid, QModelIndex* index /*out*/);

And then create your object as a reference like before:

QModelIndex *modelIndex;
getIndex(auid, modelIndex);

The downside to this though is that you'd have to change the function everywhere you use index to instead treat it like a pointer rather than reference. I find it more likely that your error may lie elsewhere in your code, and be the nature of the QModelIndex object.

score -3 · Answer 2 · answered Jun 26 '15 at 13:23

-3

The requested argument is QModelIndex&, so you can just call

QModelIndex modelIndex();
getIndex(auid, modelIndex);

Btw: QModelIndex is a really slim object which gets invalid very quickly. You should not create pointers to it without deep insight to Qt's Model/View system.

answered Jun 26 '15 at 13:23

Christian

114
6

2

No you can't. `QModelIndex modelIndex();` wont compile as it fails the most vexing parse. – NathanOliver Jun 26 '15 at 13:24
Well, then `QModelIndex modelIndex;`. `getIndex(auid, QModelIndex())` is better anyway. – Christian Jun 26 '15 at 13:25

How do I declare a object for use with this function

2 Answers2