C++ (Qt)
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QWidget>
#include <QTextEdit>
#include <QTextStream>
#include <QPushButton>
 
class MainWindow : public QWidget
{
    Q_OBJECT
 
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
private:
    QTextEdit * textEdit;
 
    QPushButton * buttonOpen;
    QPushButton * buttonSave;
 
public slots:
    void open();
    void save();
};
 
#endif // MAINWINDOW_H
 

C++ (Qt)
#include "mainwindow.h"
 
#include <QVBoxLayout>
#include <QHBoxLayout>
#include <QMessageBox>
#include <QFileDialog>
#include <QTextStream>
 
 
MainWindow::MainWindow(QWidget *parent)
    : QWidget(parent)
{
    textEdit = new QTextEdit();
 
    buttonOpen = new QPushButton("Open");
    connect(buttonOpen, SIGNAL(clicked()), SLOT(open()));
 
    buttonSave = new QPushButton("Save");
    connect(buttonSave, SIGNAL(clicked()), SLOT(save()));
 
    QHBoxLayout * buttonsLayout = new QHBoxLayout();
    buttonsLayout->addWidget(buttonOpen);
    buttonsLayout->addWidget(buttonSave);
 
    QVBoxLayout * layout = new QVBoxLayout();
    layout->addLayout(buttonsLayout);
    layout->addWidget(textEdit);
 
    setLayout(layout);
}
 
MainWindow::~MainWindow()
{
 
}
 
void MainWindow::open() {
    const QString& fileName = QFileDialog::getOpenFileName(this);
    if (fileName.isEmpty()) {
        return;
    }
 
    QFile file(fileName);
    if (file.open(QIODevice::ReadOnly)) {
        QTextStream in(&file);
        textEdit->setText(in.readAll());
    } else {
        QMessageBox::warning(this, "Warn", file.errorString());
    }
}
 
void MainWindow::save() {
    const QString& fileName = QFileDialog::getSaveFileName(this);
    if (fileName.isEmpty()) {
        return;
    }
 
    QFile file(fileName);
    if (file.open(QIODevice::WriteOnly)) {
        QTextStream out(&file);
        out << textEdit->toHtml();
    } else {
        QMessageBox::warning(this, "Warn", file.errorString());
    }
}