为什么我在关于文件编码格式的qt代码中得到了凌乱的代码结果?

我最近想学习qt如何对文件进行编码和解码。我测试了一些例子,但有些让我感到困惑。

这是我的代码:

#include <QApplication>
#include <QFile>
#include <QTextStream>

#define TEST(testFile) void test##testFile()

TEST(ANSI)
{
    QFile inFile(":/test/test-ANSI.txt");
    if (!inFile.open(QIODevice::ReadOnly | QIODevice::Text))
        return;

    QFile outFile("../test-ANSI-bak.txt");
    if (!outFile.open(QIODevice::WriteOnly | QIODevice::Truncate))
        return;

    QTextStream in(&inFile);
    QTextStream out(&outFile);
    out.setCodec("UTF-8");

    // 这样写入会去掉换行符号
    while (!in.atEnd()) {
        QString line = in.readLine();
        out << line;
    }
}

TEST(GB2312)
{
    QFile inFile(":/test/test-GB2312.txt");
    if (!inFile.open(QIODevice::ReadOnly | QIODevice::Text))
        return;

    QFile outFile("../test-GB2312-bak.txt");
    if (!outFile.open(QIODevice::WriteOnly | QIODevice::Truncate))
        return;

    QTextStream in(&inFile);
    QTextStream out(&outFile);
    out.setCodec("UTF-8");

    while (!in.atEnd()) {
        QString line = in.readLine();
        out << line;
    }
}

TEST(utf8BOM)
{
    QFile inFile(":/test/test-utf8-BOM.txt");
    if (!inFile.open(QIODevice::ReadOnly | QIODevice::Text))
        return;

    QFile outFile("../test-utf8-BOM-bak.txt");
    if (!outFile.open(QIODevice::WriteOnly | QIODevice::Truncate))
        return;

    QTextStream in(&inFile);
    QTextStream out(&outFile);
    out.setCodec("UTF-8");

    while (!in.atEnd()) {
        QString line = in.readLine();
        out << line;
    }
}

TEST(utf8)
{
    QFile inFile(":/test/test-utf8.txt");
    if (!inFile.open(QIODevice::ReadOnly | QIODevice::Text))
        return;

    QFile outFile("../test-utf8-bak.txt");
    if (!outFile.open(QIODevice::WriteOnly | QIODevice::Truncate))
        return;

    QTextStream in(&inFile);
    QTextStream out(&outFile);
    out.setCodec("UTF-8");

    while (!in.atEnd()) {
        QString line = in.readLine();
        out << line;
    }
}

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

    testANSI();
    testGB2312();
    testutf8BOM();
    testutf8();

    return app.exec();
}

我的输入文本内容如下:

----
I love you!
我爱你！
。。。
1234
1234

对于ANSI、GB2312、utf8 BOM,我得到了输出文件 例如:测试ANSI bak。txt文件

----I love you!我爱你！。。。12341234

对于utf8,我得到了输出文件 例如:test-utf8-bak。txt文件

----I love you!鎴戠埍浣狅紒銆傘€傘€12341234

为什么test-utf8-bak。txt显示凌乱的代码?我很困惑!