QVector<QString> reference count crashing

user4592357

in a game i use Builder design pattern. The game has categories and each category has some properties associated with it (pictures, category name, category related file path):

struct CategoryProperties {
	QString m_propertyName;
	QString m_wordsFilePath;
	QVector<QString> m_iconPaths;
};

here's the base builder class:

#include "categoryProperties.h"

class PropertiesBuilder {
public:
	virtual ~PropertiesBuilder() = 0;

	virtual void setPropertyName() = 0;
	virtual void setWordsFilePath() = 0;
	virtual void setIconPaths() = 0;

	CategoryProperties *getPropertiesPtr() const { return m_properties; }

protected:
	CategoryProperties *m_properties;
};

inline PropertiesBuilder::~PropertiesBuilder() {}

and this is one of its derived classes:

// .h
#include "propertiesBuilder.h"

class MapBuilder : public PropertiesBuilder {
public:
	MapBuilder();
	~MapBuilder() override;

	void setPropertyName() override;
	void setWordsFilePath() override;
	void setIconPaths() override;
};

// .cpp
#include "mapBuilder.h"
#include "propertiesBuilder.h"
#include "categoryProperties.h"

MapBuilder::MapBuilder() {
	m_properties = new CategoryProperties;
}

MapBuilder::~MapBuilder() {
	delete m_properties;
}

void MapBuilder::setPropertyName() {
	m_properties->m_propertyName = "map";
}

void MapBuilder::setWordsFilePath() {
	m_properties->m_wordsFilePath = "words/geography.txt";
}

void MapBuilder::setIconPaths() {
	m_properties->m_iconPaths.reserve(6);
	for(auto i = 0; i < 6; ++i)
		m_properties->m_iconPaths.push_back(":/map/map_" + QString::number(i));
}

then i have a widget (which is the Director of Builder pattern), where i have buttons - one for each category:

class CategoriesPage : public QWidget {
	Q_OBJECT
public:
        // ...
private slots:
	void onMapBtnClicked();
private:
	// category page properties
	PropertiesBuilder *m_pPropBuilder;
	CategoryProperties *m_pCategoryProps;
};

// Map button
const auto mapBtn = new CategoryButton { ":/map/map_0", "Geography", sMapToolTip, this };
connect(mapBtn, &QAbstractButton::clicked, this, &CategoriesPage::onMapBtnClicked);

the slot:

void CategoriesPage::onMapBtnClicked() {
	if(m_pPropBuilder) delete m_pPropBuilder;
	//if(m_pCategoryProps) delete m_pCategoryProps;
	m_pPropBuilder = new MapBuilder;
	setCategoryProperties();
	m_pCategoryProps = dynamic_cast<MapBuilder *>(m_pPropBuilder)->getPropertiesPtr();
}

the slots for other categories are similar.

now, the problem is, when a button is clicked, everything is okay. the category is properly set up. but when i click another button, the program crashes. i debugged and saw that the problem was this:

if i delete m_pCategoryProps (last code snippet, commented), i get a crash on QVector, where there's something wrong with reference count (see the struct). when i commented the line, everything is okay. but there's a memory leak so it's not okay.

i've spent quite a lot time on this and couldn't figure out anything.
can someone please explain what am i doing wrong?

thanks a lot.

SGaist

Hi,

You are deleting your m_pPropBuilder which deletes its m_properties that you stored in m_pCategoryProps then you delete m_pCategoryProps so basically you are trying to delete again something that was already deleted.