TextPreview

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[toc align_right="yes" depth="3"]

TextPreview

This is an example of Qt Gui Application to read a specified number of lines or all lines from a text file, whose character set is automatically detected and displayed.

The program was developed with Qt Creator 2.7.1, and ran successfully with Qt 4.8.4 on Ubuntu 13.04, linking to a universal character detection library libuchardet available in package as libuchardet-dev. Lines for debugging are intentionally left so as to be helpful in checking the program.

Souce code

TextPreview.pro

  1. ————————————————-
  2. Project created by QtCreator 2013-09-04T00:11:05
  3. ————————————————-
QT ''= core gui

greaterThan(QT_MAJOR_VERSION, 4): QT''= widgets

TARGET = TextPreview
TEMPLATE = app

SOURCES ''= main.cpp widget.cpp

HEADERS''= widget.h

FORMS ''= widget.ui

unix|win32: LIBS''= -luchardet

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
 Q_OBJECT

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

private slots:
 void on_pushButton_clicked();

private:
 Ui::Widget *ui;
};

#endif // WIDGET_H

main.cpp

#include "widget.h"
#include <QApplication>

int main(int argc, char *argv[])
{
 QApplication a(argc, argv);
 Widget w;

 w.setWindowTitle("Text Preview");

 w.show();

 return a.exec();
}

widget.cpp

#include "widget.h"
#include "ui_widget.h"

#include <QLabel>
#include <QString>
#include <QFileDialog>
#include <QDir>
#include <QMessageBox>
#include <QTextCodec>
#include <QTextDecoder>

#include <uchardet/uchardet.h>

#include <QDebug>

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

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

void Widget::on_pushButton_clicked()
{
 // Get file name
 QString fileName = QFileDialog::getOpenFileName(this,
 tr("Open text file"), QDir::homePath(), tr("Text files ('''.txt)"));
 ui->label_4->setText(fileName); // Show file name

// Open text file
 QFile file(fileName);
 if(!file.open(QIODevice::ReadOnly | QIODevice::Text))
 return;

// Read lines
 int i = 0;
 QString lm = ui->lineEdit->text();
 int lineMax = lm.toInt(); // Maximum number of lines to be read
 qDebug() << "lineMax = " << QString::number(lineMax);
 QByteArray temp("");
 QByteArray line("");
 while (i++ < lineMax &amp;&amp; !file.atEnd())
 {
 line = file.readLine();
 temp = temp.append(line);
 }

// Detect character code set
 uchardet_t ucd = uchardet_new();
 if(uchardet_handle_data(ucd, temp, 20) != 0) // first 20 bytes used for detection
 {
 QMessageBox msg;
 msg.setText("Failed to detect character set from data.UTF-8.");
 msg.exec();
 }

uchardet_data_end(ucd);
 const char *charSetName = uchardet_get_charset(ucd);
 QString csn = charSetName;
 qDebug() << "Detected character set: " << csn;
 uchardet_delete(ucd);
 ui->label_6->setText(charSetName); // Show character code set

// Preview text
 QTextCodec *codec = QTextCodec::codecForName(charSetName); // Set codec
 QTextDecoder *decoder = codec->makeDecoder(); // Decode
 QString str = decoder->toUnicode(temp); // Get text
 ui->plainTextEdit->setPlainText(str); // Show text
}

widget.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>Widget</class>
 <widget class="QWidget" name="Widget">
 <property name="geometry">
 <rect>
 <x>0</x>
 <y>0</y>
 <width>603</width>
 <height>492</height>
 </rect>
 </property>
 <property name="windowTitle">
 <string>Widget</string>
 </property>
 <layout class="QVBoxLayout" name="verticalLayout_2">
 <item>
 <layout class="QVBoxLayout" name="verticalLayout">
 <item>
 <widget class="QLabel" name="label">
 <property name="font">
 <font>
 <pointsize>14</pointsize>
 <weight>75</weight>
 <italic>false</italic>
 <bold>true</bold>
 </font>
 </property>
 <property name="text">
 <string>Text Preview</string>
 </property>
 </widget>
 </item>
 <item>
 <layout class="QHBoxLayout" name="horizontalLayout">
 <item>
 <widget class="QPushButton" name="pushButton">
 <property name="text">
 <string>Preview</string>
 </property>
 </widget>
 </item>
 <item>
 <widget class="QLineEdit" name="lineEdit">
 <property name="text">
 <string>10</string>
 </property>
 </widget>
 </item>
 <item>
 <widget class="QLabel" name="label_2">
 <property name="text">
 <string>lines</string>
 </property>
 </widget>
 </item>
 <item>
 <spacer name="horizontalSpacer">
 <property name="orientation">
 <enum>Qt::Horizontal</enum>
 </property>
 <property name="sizeHint" stdset="0">
 <size>
 <width>288</width>
 <height>20</height>
 </size>
 </property>
 </spacer>
 </item>
 </layout>
 </item>
 <item>
 <layout class="QHBoxLayout" name="horizontalLayout_2">
 <item>
 <widget class="QLabel" name="label_3">
 <property name="minimumSize">
 <size>
 <width>0</width>
 <height>0</height>
 </size>
 </property>
 <property name="maximumSize">
 <size>
 <width>70</width>
 <height>16777215</height>
 </size>
 </property>
 <property name="text">
 <string>File name: </string>
 </property>
 </widget>
 </item>
 <item>
 <widget class="QLabel" name="label_4">
 <property name="text">
 <string/>
 </property>
 </widget>
 </item>
 </layout>
 </item>
 <item>
 <layout class="QHBoxLayout" name="horizontalLayout_3">
 <item>
 <widget class="QLabel" name="label_5">
 <property name="text">
 <string>Character code set: </string>
 </property>
 </widget>
 </item>
 <item>
 <widget class="QLabel" name="label_6">
 <property name="text">
 <string/>
 </property>
 </widget>
 </item>
 <item>
 <spacer name="horizontalSpacer_2">
 <property name="orientation">
 <enum>Qt::Horizontal</enum>
 </property>
 <property name="sizeHint" stdset="0">
 <size>
 <width>228</width>
 <height>20</height>
 </size>
 </property>
 </spacer>
 </item>
 </layout>
 </item>
 <item>
 <layout class="QHBoxLayout" name="horizontalLayout_4">
 <item>
 <widget class="QLabel" name="label_7">
 <property name="text">
 <string>Text: </string>
 </property>
 </widget>
 </item>
 <item>
 <spacer name="horizontalSpacer_3">
 <property name="orientation">
 <enum>Qt::Horizontal</enum>
 </property>
 <property name="sizeHint" stdset="0">
 <size>
 <width>478</width>
 <height>20</height>
 </size>
 </property>
 </spacer>
 </item>
 </layout>
 </item>
 <item>
 <widget class="QPlainTextEdit" name="plainTextEdit">
 <property name="readOnly">
 <bool>true</bool>
 </property>
 </widget>
 </item>
 </layout>
 </item>
 </layout>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>

Gui design (widget.ui)

Picture of Gui Design in Qt Creator for widget.ui

Example

Ran the program.

Picture of a widget window when the TextPreview program is launched.

Changed the number of lines to 2, and hit the Preview button. Chose a text file in a dialog box.

Picture of the widget window after pushing the preview button and choosing a text file.

The file's path and character set are shown, and the first 2 lines, as specified, are shown in the plain text box.

Links