[Kommander-devel] Questions for seasoned C++ gurus

[Andras Mantia]

Hi,

On Tuesday 01 April 2008, Eric Laffoon wrote:
> Hi All,
> I'm rewriting the database plugin for my immediate production use as
> a more robust and flexible tool, and to make a path to port to KDE4.

Good idea.


> private:
>   QSqlDatabase* db;
>   QSqlQuery* query;

I checked out the code and tries to compile. I think the base problem is 
that you programmed too much in php and too little in C++.
"QSqlDatabase * db" means  "db" is a pointer to a QSqlDatabase object 
and should be allocated on the heap with "new" (or with a method that 
returns " QSqlDatabase* "). You can access the methods with 
db->methodname().

QSqlDatabase db on the other hand creates the db object right away at 
that place (so usually you need QSqlDatabase 
db(arguments_of_the_constructor) ) and as this isn't a pointer, you 
access the methods with:
db.methodname().

This was the main problem, mixing pointers and none-pointers.

Now if you get an error like:
/data/development/sources/kommander-
plugins/database3/src/database.cpp:228: error: passing 'const QSqlQuery' 
as 'this' argument of 'virtual bool QSqlQuery::next()' discards 
qualifiers

it usually means you are treating some const variable as none-const (or 
vice versa), or you access none-const variables from const methods. Here 
that is the problem.

One other thing I noticed was that even though you had a 
QSqlDatabase * db member variable, when you assigned a value to it, you 
declared again. That means that the value was assigned to a local db 
pointer => crash in all other places where you use db->something.

So should I fix these issues or will you? ;)

Andras


-- 
 
Quanta Plus developer - http://quanta.kdewebdev.org
K Desktop Environment - http://www.kde.org
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