Qt5 Gui program compiles but generates segmentation fault.

hbsplitter.cpp

/* file : hbsplitter.cpp */

#include <QHBoxLayout>
#include <QSplitter>
#include <QString>

#include "hbsplitter.h"

#include "mlabelwidget.h"
#include "mtextedit.h"

Hbsplitter::Hbsplitter(QWidget *parent) : QWidget(parent)
{
  QHBoxLayout *hbox = new QHBoxLayout(this);
  QSplitter *splitter1 = new QSplitter(Qt::Horizontal);
  Mtextedit *myMtextedit = new Mtextedit();
  Mlabelwidget *myMlabelwidget = new Mlabelwidget();
  QString newLabel;
  newLabel = "Qt with cpp.";
  myMlabelwidget->show();
  myMlabelwidget->changeText(newLabel);
  /* if I uncomment the above line I get "zsh: segmentation fault  ./stage3"
   * where stage3 is the name of the executable */
  splitter1->addWidget(myMtextedit);
  splitter1->addWidget(myMlabelwidget);
  hbox->addWidget(splitter1);
}

hbsplitter.h

/* file : hbsplitter.h */

#pragma once

#include <QWidget>

class Hbsplitter : public QWidget
{
  public:
    Hbsplitter(QWidget *parent = 0);
};

main.cpp

/* file : main.cpp */

#include <QApplication>

#include "hbsplitter.h"

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);

  app.setStyleSheet("QSplitter::handle { background-color: #333;}");

  Hbsplitter window;

  window.resize(700, 300);
  window.setWindowTitle("Notes to SVG");
  window.show();

  return app.exec();
}

mlabelwidget.cpp

/* file : mlabelwidget.cpp */

#include <QWidget>
#include <QHBoxLayout>
#include <QLabel>
#include <iostream>
#include "mlabelwidget.h"

Mlabelwidget::Mlabelwidget(QWidget *parent) : QWidget(parent)
{
  QHBoxLayout *hbox = new QHBoxLayout(this);
  QLabel *label = new QLabel();
  label->setText("This is Qt");
  hbox->addWidget(label);
}

void Mlabelwidget::changeText(QString input) {
  std::cout << "Mlabelwidget::changeText() called." << "\n";
  /* std::cout << input << "\n"; */
  label->setText(input); 
  std::cout << "Mlabelwidget::changeText() completed." << "\n";
}

mlabelwidget.h

/* file : mlabelwidget.h */

#pragma once

#include <QWidget>
#include <QLabel>

class Mlabelwidget : public QWidget
{
  public:
    Mlabelwidget(QWidget *parent = 0);
    QLabel *label;
    void changeText(QString input);
};

mtextedit.cpp

/* file : mtextedit.cpp */

#include <QWidget>
#include <QHBoxLayout>
#include <QTextEdit>

#include "mtextedit.h"

Mtextedit::Mtextedit(QWidget *parent) : QWidget(parent)
{
  QHBoxLayout *hbox = new QHBoxLayout(this);

  QTextEdit *mtextedit = new QTextEdit();
  hbox->addWidget(mtextedit);
}

mtextedit.h

/* file : mtextedit.h */

#pragma once

#include <QWidget>

class Mtextedit : public QWidget
{
  public:
    Mtextedit(QWidget *parent = 0);
};

stage3.pro

######################################################################
# Automatically generated by qmake (3.0) Tue Jul 2 04:42:55 2019
######################################################################

TEMPLATE = app
TARGET = stage3
INCLUDEPATH += .

# Input
HEADERS += hbsplitter.h mlabelwidget.h mtextedit.h
SOURCES += hbsplitter.cpp main.cpp mlabelwidget.cpp mtextedit.cpp

QT += widgets svg