Hello:
It's time again to play Find-That-Bug:
I just spent several days tracking down a bug in the following code.
It was difficult to find because it is a reduced probability,
data-specific event; It can be completely function,
completely dysfunctional, and all shades in between.
I am using Qt 4.7.1
Let's assume all of the input strings are ASCII.
Can you find it?
QString
MakeDigest( QStringList list ) {
QCryptographicHash ch(QCryptographicHash::Md5);
foreach( QString s, list )
ch.addData( s.toAscii() );
return ch.result();
}
----------------------------
Scroll down if you need a hint.
If you need a hint, run this code:
for( int i=60; i<70; i++ ) {
QStringList list; list << QString::number(i) << QString::number(i);
QString d = MakeDigest(list);
qDebug() << "digest size: " << i << ' ' << 8 * d.size();
}
------------------------------------
If you need another hint, see the description of this:
QString::QString ( const QByteArray &ba )
I take issue with the behavior of this constructor
because we know the length of ba and QStrings can contain QChar('\0').
While there is probably a good reason for the behavior,
I did not see it coming.
I tend to use QStrings over QByteArrays as QStrings
provide more operations.
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