diff --git a/src/kdefrontend/datasources/MQTTHelpers.cpp b/src/kdefrontend/datasources/MQTTHelpers.cpp
index e05839f1b..1ca59869d 100644
--- a/src/kdefrontend/datasources/MQTTHelpers.cpp
+++ b/src/kdefrontend/datasources/MQTTHelpers.cpp
@@ -1,369 +1,369 @@
 /***************************************************************************
     File                 : MQTTHelpers.cpp
     Project              : LabPlot
     Description          : MQTT related helper functions
     --------------------------------------------------------------------
     Copyright            : (C) 2019 Alexander Semke (alexander.semke@web.de)
  ***************************************************************************/
 
 /***************************************************************************
  *                                                                         *
  *  This program is free software; you can redistribute it and/or modify   *
  *  it under the terms of the GNU General Public License as published by   *
  *  the Free Software Foundation; either version 2 of the License, or      *
  *  (at your option) any later version.                                    *
  *                                                                         *
  *  This program is distributed in the hope that it will be useful,        *
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of         *
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the          *
  *  GNU General Public License for more details.                           *
  *                                                                         *
  *   You should have received a copy of the GNU General Public License     *
  *   along with this program; if not, write to the Free Software           *
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor,                    *
  *   Boston, MA  02110-1301  USA                                           *
  *                                                                         *
  ***************************************************************************/
 
 #include "MQTTHelpers.h"
 
 #include <QTreeWidgetItem>
 #include <QStringList>
 
 /*!
  *\brief Adds to a # wildcard containing topic, every topic present in twTopics that the former topic contains
  *
  * \param topic pointer to the TreeWidgetItem which was selected before subscribing
  * \param subscription pointer to the TreeWidgetItem which represents the new subscirption,
  *		  we add all of the children to this item
  */
 void MQTTHelpers::addSubscriptionChildren(QTreeWidgetItem* topic, QTreeWidgetItem* subscription) {
 	//if the topic doesn't have any children we don't do anything
 	if (topic->childCount() <= 0)
 		return;
 
 	for (int i = 0; i < topic->childCount(); ++i) {
 		QTreeWidgetItem* temp = topic->child(i);
 		QString name;
 		//if it has children, then we add it as a # wildcrad containing topic
 		if (topic->child(i)->childCount() > 0) {
 			name.append(temp->text(0) + "/#");
 			while (temp->parent() != nullptr) {
 				temp = temp->parent();
 				name.prepend(temp->text(0) + '/');
 			}
 		}
 
 		//if not then we simply add the topic itself
 		else {
 			name.append(temp->text(0));
 			while (temp->parent() != nullptr) {
 				temp = temp->parent();
 				name.prepend(temp->text(0) + '/');
 			}
 		}
 
 		QStringList nameList;
 		nameList.append(name);
 		QTreeWidgetItem* childItem = new QTreeWidgetItem(nameList);
 		subscription->addChild(childItem);
 		//we use the function recursively on the given item
 		addSubscriptionChildren(topic->child(i), childItem);
 	}
 }
 
 /*!
  *\brief Restores the children of a top level item in twSubscriptions if it contains wildcards
  *
  * \param topic pointer to a top level item in twTopics which represents the root of the subscription topic
  * \param subscription pointer to a top level item in twSubscriptions, this is the item whose children will be restored
  * \param list QStringList containing the levels of the subscription topic
  * \param level the level's number which is being investigated
  */
 void MQTTHelpers::restoreSubscriptionChildren(QTreeWidgetItem * topic, QTreeWidgetItem * subscription, const QStringList& list, int level) {
-	if (list[level] != '+' && list[level] != "#" && level < list.size() - 1) {
+	if (list[level] != "+" && list[level] != "#" && level < list.size() - 1) {
 		for (int i = 0; i < topic->childCount(); ++i) {
 			//if the current level isn't + or # wildcard we recursively continue with the next level
 			if (topic->child(i)->text(0) == list[level]) {
 				restoreSubscriptionChildren(topic->child(i), subscription, list, level + 1);
 				break;
 			}
 		}
-	} else if (list[level] == '+') {
+	} else if (list[level] == "+") {
 		for (int i = 0; i < topic->childCount(); ++i) {
 			//determine the name of the topic, contained by the subscription
 			QString name;
 			name.append(topic->child(i)->text(0));
 			for (int j = level + 1; j < list.size(); ++j) {
 				name.append('/' + list[j]);
 			}
 			QTreeWidgetItem* temp = topic->child(i);
 			while (temp->parent() != nullptr) {
 				temp = temp->parent();
 				name.prepend(temp->text(0) + '/');
 			}
 
 			//Add the topic as child of the subscription
 			QStringList nameList;
 			nameList.append(name);
 			QTreeWidgetItem* newItem = new QTreeWidgetItem(nameList);
 			subscription->addChild(newItem);
 			//Continue adding children recursively to the new item
 			restoreSubscriptionChildren(topic->child(i), newItem, list, level + 1);
 		}
 	} else if (list[level] == "#") {
 		//add the children of the # wildcard containing subscription
 		MQTTHelpers::addSubscriptionChildren(topic, subscription);
 	}
 }
 
 /*!
  *\brief Returns the amount of topics that the '+' wildcard will replace in the level position
  *
  * \param levelIdx the level currently being investigated
  * \param level the level where the new + wildcard will be placed
  * \param commonList the topic name split into levels
  * \param currentItem pointer to a TreeWidgetItem which represents the parent of the level
  *		  represented by levelIdx
  * \return returns the childCount, or -1 if some topics already represented by + wildcard have different
  *		   amount of children
  */
 int MQTTHelpers::checkCommonChildCount(int levelIdx, int level, QStringList& commonList, QTreeWidgetItem* currentItem) {
 	//we recursively check the number of children, until we get to level-1
 	if (levelIdx < level - 1) {
-		if (commonList[levelIdx] != '+') {
+		if (commonList[levelIdx] != "+") {
 			for (int j = 0; j < currentItem->childCount(); ++j) {
 				if (currentItem->child(j)->text(0) == commonList[levelIdx]) {
 					//if the level isn't represented by + wildcard we simply return the amount of children of the corresponding item, recursively
 					return checkCommonChildCount(levelIdx + 1, level, commonList, currentItem->child(j));
 				}
 			}
 		} else {
 			int childCount = -1;
 			bool ok = true;
 
 			//otherwise we check if every + wildcard represented topic has the same number of children, recursively
 			for (int j = 0; j < currentItem->childCount(); ++j) {
 				int temp = checkCommonChildCount(levelIdx + 1, level, commonList, currentItem->child(j));
 				if ((j > 0) && (temp != childCount)) {
 					ok = false;
 					break;
 				}
 				childCount = temp;
 			}
 
 			//if yes we return this number, otherwise -1
 			if (ok)
 				return childCount;
 			else
 				return -1;
 		}
 	} else if (levelIdx == level - 1) {
-		if (commonList[levelIdx] != '+') {
+		if (commonList[levelIdx] != "+") {
 			for (int j = 0; j < currentItem->childCount(); ++j) {
 				if (currentItem->child(j)->text(0) == commonList[levelIdx]) {
 					//if the level isn't represented by + wildcard we simply return the amount of children of the corresponding item
 					return currentItem->child(j)->childCount();
 				}
 			}
 		} else {
 			int childCount = -1;
 			bool ok = true;
 
 			//otherwise we check if every + wildcard represented topic has the same number of children
 			for (int j = 0; j < currentItem->childCount(); ++j) {
 				if ((j > 0) && (currentItem->child(j)->childCount() != childCount)) {
 					ok = false;
 					break;
 				}
 				childCount = currentItem->child(j)->childCount();
 			}
 
 			//if yes we return this number, otherwise -1
 			if (ok)
 				return childCount;
 			else
 				return -1;
 		}
 
 	} else if (level == 1 && levelIdx == 1)
 		return currentItem->childCount();
 
 	return -1;
 }
 
 
 /*!
  *\brief Returns the index of level where the two topic names differ, if there is a common topic for them
  *
  * \param first the name of a topic
  * \param second the name of a topic
  * \return The index of the unequal level, if there is a common topic, otherwise -1
  */
 int MQTTHelpers::commonLevelIndex(const QString& first, const QString& second) {
 	QStringList firstList = first.split('/', QString::SkipEmptyParts);
 	QStringList secondtList = second.split('/', QString::SkipEmptyParts);
 	QString commonTopic = "";
 	int differIndex = -1;
 
 	if (!firstList.isEmpty()) {
 		//the two topics have to be the same size and can't be identic
 		if (firstList.size() == secondtList.size() && (first != second))	{
 
 			//the index where they differ
 			for (int i = 0; i < firstList.size(); ++i) {
 				if (firstList.at(i) != secondtList.at(i)) {
 					differIndex = i;
 					break;
 				}
 			}
 
 			//they can differ at only one level
 			bool differ = false;
 			if (differIndex > 0) {
 				for (int j = differIndex + 1; j < firstList.size(); ++j) {
 					if (firstList.at(j) != secondtList.at(j)) {
 						differ = true;
 						break;
 					}
 				}
 			}
 			else
 				differ = true;
 
 			if (!differ) {
 				for (int i = 0; i < firstList.size(); ++i) {
 					if (i != differIndex)
 						commonTopic.append(firstList.at(i));
 					else
 						commonTopic.append('+');
 
 					if (i != firstList.size() - 1)
 						commonTopic.append('/');
 				}
 			}
 		}
 	}
 
 	//if there is a common topic we return the differIndex
 	if (!commonTopic.isEmpty())
 		return differIndex;
 	else
 		return -1;
 }
 
 /*!
  *\brief Returns the '+' wildcard containing topic name, which includes the given topic names
  *
  * \param first the name of a topic
  * \param second the name of a topic
  * \return The name of the common topic, if it exists, otherwise ""
  */
 QString MQTTHelpers::checkCommonLevel(const QString& first, const QString& second) {
 	const QStringList& firstList = first.split('/', QString::SkipEmptyParts);
 	if (firstList.isEmpty())
 		return QString();
 
 	const QStringList& secondtList = second.split('/', QString::SkipEmptyParts);
 	QString commonTopic = "";
 
 	//the two topics have to be the same size and can't be identic
 	if (firstList.size() == secondtList.size() && (first != second))	{
 
 		//the index where they differ
 		int differIndex = -1;
 		for (int i = 0; i < firstList.size(); ++i) {
 			if (firstList.at(i) != secondtList.at(i)) {
 				differIndex = i;
 				break;
 			}
 		}
 
 		//they can differ at only one level
 		bool differ = false;
 		if (differIndex > 0) {
 			for (int j = differIndex + 1; j < firstList.size(); ++j) {
 				if (firstList.at(j) != secondtList.at(j)) {
 					differ = true;
 					break;
 				}
 			}
 		} else
 			differ = true;
 
 		if (!differ) {
 			for (int i = 0; i < firstList.size(); ++i) {
 				if (i != differIndex) {
 					commonTopic.append(firstList.at(i));
 				} else {
 					//we put '+' wildcard at the level where they differ
 					commonTopic.append('+');
 				}
 
 				if (i != firstList.size() - 1)
 					commonTopic.append('/');
 			}
 		}
 	}
 
 // 	qDebug() << "Common topic for " << first << " and " << second << " is: " << commonTopic;
 	return commonTopic;
 }
 
 
 /*!
  *\brief Fills the children vector, with the root item's (twSubscriptions) leaf children (meaning no wildcard containing topics)
  *
  * \param children vector of TreeWidgetItem pointers
  * \param root pointer to a TreeWidgetItem of twSubscriptions
  */
 void MQTTHelpers::findSubscriptionLeafChildren(QVector<QTreeWidgetItem *>& children, QTreeWidgetItem* root) {
 	if (root->childCount() == 0)
 		children.push_back(root);
 	else
 		for (int i = 0; i < root->childCount(); ++i)
 			findSubscriptionLeafChildren(children, root->child(i));
 }
 
 /*!
  *\brief Checks if a topic contains another one
  *
  * \param superior the name of a topic
  * \param inferior the name of a topic
  * \return	true if superior is equal to or contains(if superior contains wildcards) inferior,
  *			false otherwise
  */
 bool MQTTHelpers::checkTopicContains(const QString& superior, const QString& inferior) {
 	if (superior == inferior)
 		return true;
 
 	if (!superior.contains('/'))
 		return false;
 
 	const QStringList& superiorList = superior.split('/', QString::SkipEmptyParts);
 	const QStringList& inferiorList = inferior.split('/', QString::SkipEmptyParts);
 
 	//a longer topic can't contain a shorter one
 	if (superiorList.size() > inferiorList.size())
 		return false;
 
 	bool ok = true;
 	for (int i = 0; i < superiorList.size(); ++i) {
 		if (superiorList.at(i) != inferiorList.at(i)) {
-			if ((superiorList.at(i) != '+') &&
+			if ((superiorList.at(i) != "+") &&
 					!(superiorList.at(i) == "#" && i == superiorList.size() - 1)) {
 				//if the two topics differ, and the superior's current level isn't + or #(which can be only in the last position)
 				//then superior can't contain inferior
 				ok = false;
 				break;
-			} else if (i == superiorList.size() - 1 && (superiorList.at(i) == '+' && inferiorList.at(i) == "#") ) {
+			} else if (i == superiorList.size() - 1 && (superiorList.at(i) == "+" && inferiorList.at(i) == "#") ) {
 				//if the two topics differ at the last level
 				//and the superior's current level is + while the inferior's is #(which can be only in the last position)
 				//then superior can't contain inferior
 				ok = false;
 				break;
 			}
 		}
 	}
 	return ok;
 }