Qt读取UTF8与GBK格式文件乱码问题

QFile file("GBK.txt");
file.open(QFile::ReadOnly | QFile::Text);
QTextCodec *codec = QTextCodec::codecForName("GBK");
QString content = codec->toUnicode(file.readAll());
qDebug()<<"Display GBK.txt file"<<content;

QFile file("UTF8.txt");
file.open(QFile::ReadOnly | QFile::Text);
QTextCodec *codec = QTextCodec::codecForName("UTF8");
QString content = codec->toUnicode(file.readAll());
qDebug()<<"Display UTF8.txt File: "<<content;

Display GBK.txt file "Hello world
中文
" 
Display UTF8.txt File:  "Hello world
你好
"

#include <QCoreApplication>
#include <QFile>
#include <QTextCodec>
#include <QDebug>

static void displayGBKFile()
{
    QFile file("GBK.txt");
    file.open(QFile::ReadOnly | QFile::Text);
    QTextCodec *codec = QTextCodec::codecForName("GBK");
    QString content = codec->toUnicode(file.readAll());
    qDebug()<<"Display GBK.txt file"<<content;
}

static void displayUTF8File()
{
    QFile file("UTF8.txt");
    file.open(QFile::ReadOnly | QFile::Text);
    QTextCodec *codec = QTextCodec::codecForName("UTF8");
    QString content = codec->toUnicode(file.readAll());
    qDebug()<<"Display UTF8.txt File: "<<content;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    displayGBKFile();
    displayUTF8File();

    return a.exec();
}

https://github.com/myqtdemo/QtUTF8AndGBKCoding.git