i write a test program whit QDatastream read and write the binary file but it's dif

[tsuibin]

i write a test program whit QDatastream
read and write the binary file
but
it's different

my code

QFile file("1.png");
    file.open(QIODevice::ReadOnly);
    QFile tmp("2");
    tmp.open(QIODevice::WriteOnly);
    QDataStream out(&tmp);
    out << file.readAll();

QFile file("1.png");
    file.open(QIODevice::ReadOnly);
    QFile tmp("2");
    tmp.open(QIODevice::WriteOnly);
    QDataStream out(&tmp);
    out << file.readAll();

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diff 1.png 2
output:
Binary files 1.png and 2 differ
why ?