maindiary.cpp:
void MainDiary::on_EditButton_clicked() { // here we will control what the edit button does
    /* in this function we will do the following:
     * - show the edit dialog
     * - retrieve all local entries (they will be stored in %userprofile%\diary)
     * - display all these entries in a formated matter
     */
    QWidget* Edit = new QWidget(); // set an object for our new window
    Edit->show();
    //Edit.ParseFile(); // retrieve each local file
    qDebug("done");

}

maindiary.h:
#ifndef MAINDIARY_H
#define MAINDIARY_H

#include <QMainWindow>

namespace Ui {
class MainDiary;
}

class MainDiary : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainDiary(QWidget *parent = 0);
    ~MainDiary();

private slots:
    void on_EditButton_clicked();

    void on_NewButton_clicked();

private:
    Ui::MainDiary *ui;
};

#endif // MAINDIARY_H


edidiaryentry.cpp:
#include "editdiaryentry.h"
#include "ui_editdiaryentry.h"

EditDiaryEntry::EditDiaryEntry(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::EditDiaryEntry) {
    ui->setupUi(this);
}

EditDiaryEntry::~EditDiaryEntry(){
    delete ui;
}

editdiaryentry.h:
#ifndef EDITDIARYENTRY_H
#define EDITDIARYENTRY_H

#include <QWidget>

namespace Ui {
class EditDiaryEntry;
}

class EditDiaryEntry : public QWidget
{
    Q_OBJECT

public:
    explicit EditDiaryEntry(QWidget *parent = 0);
    ~EditDiaryEntry();

private:
    Ui::EditDiaryEntry *ui;
};

#endif // EDITDIARYENTRY_H