Setting QSharedPointer

Question

I'm coming from a C# background and still getting my head around c++ and Qt smart pointers. This should be a basic question:

In myClass.h

QSharedPointer<AccessFlags> m_flags;

In myClass.cpp I'm trying to set (is set the correct word?) the m_flags pointer

if(m_flags.isNull())
    m_flags = new AccessFlags();


class AccessFlags{
public:
     QHash<QString,int> flags;
     AccessFlags();  //The dictionary is setup in the constructor
};

The compiler complains "no match for 'operator=' in.. How do I set the pointer?

Why is there a `.` after `m_flags`? – David Schwartz Nov 06 '12 at 02:07 — David Schwartz, Nov 06 '12 at 02:07
typo. Didn't copy and paste code. – DarwinIcesurfer Nov 06 '12 at 02:10 — DarwinIcesurfer, Nov 06 '12 at 02:10

Fraser · Accepted Answer · 2012-11-06T02:14:11.233

6

You're trying to assign a raw pointer to a QSharedPointer in the line

m_flags = new AccessFlags();

You probably want something like

m_flags = QSharedPointer<AccessFlags>(new AccessFlags);

edited Nov 06 '12 at 02:14

answered Nov 06 '12 at 02:07

Fraser

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score 5 · Answer 2 · answered Nov 06 '12 at 10:40

5

Consider using std::shared_ptr instead QSharedPointer if you work with modern C++11 compiler (e.g. GCC 4.6 or above and MSVC 10.0).

First of all, it's a standard and second thing, you could use std::make_shared to init your pointer which can be faster! (For example, in MSVS2010/2012 allocation occurs only once for make_shared instead two allocations: one for new and one for internal counter).

answered Nov 06 '12 at 10:40

Eugene Mamin

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There is a static `create` method, which makes the same as `std::make_shared`, so no gain here. And if the whole project uses QT classes, there is no reason to create a mess with standard classes and then have a pain converting one class objects to another. – rightaway717 May 05 '17 at 21:01
For the record: `create` method is only available in Qt5 – tobilocker Sep 25 '18 at 12:49

Setting QSharedPointer

2 Answers2