<![CDATA[porting to QRandomGenerator]]>I am porting some old code under qt 5.15.2.

qsrand(30);
qDebug() << "qrand" << qrand();
qDebug() << "qrand" << qrand();
qDebug() << "qrand" << qrand();

this code always gives me the same result. With the same result I mean the same sequence. In the new code I have written:

QRandomGenerator generator;
generator.seed(30);

qDebug() << "randomGenerator" << randGenerator.bounded(RAND_MAX);
qDebug() << "randomGenerator" << randGenerator.bounded(RAND_MAX);
qDebug() << "randomGenerator" << randGenerator.bounded(RAND_MAX);

this too has always the same result but the values ​​are different from the previous case. can i have the same result of the old qrand?

]]>https://forum.qt.io/topic/127019/porting-to-qrandomgeneratorRSS for NodeTue, 05 May 2026 18:29:42 GMTWed, 26 May 2021 14:42:02 GMT60<![CDATA[Reply to porting to QRandomGenerator on Wed, 26 May 2021 15:55:54 GMT]]>@Massimiliano75 said in porting to QRandomGenerator:

can i have the same result of the old qrand?

You really should understand what 'random' means...

]]>https://forum.qt.io/post/661739https://forum.qt.io/post/661739Wed, 26 May 2021 15:55:54 GMT<![CDATA[Reply to porting to QRandomGenerator on Wed, 26 May 2021 15:00:10 GMT]]>@Massimiliano75 said in porting to QRandomGenerator:

can i have the same result of the old qrand?

I have no evidence for my answer, but I am interested in anything to do with random & pseudo-random numbers.

I would very much doubt that you can use the same seed, or even any other seed, to generate the same sequence as it used to be. I would imagine these two use different pseudo-generator algorithms, and hence won't produce the same sequences as each other. Seed or not.

I guess this could be a problem when upgrading for testing (with existing result sets), but haven't seen a comment about this.

Unless someone who knows the changed code tells you otherwise... :)

]]>https://forum.qt.io/post/661723https://forum.qt.io/post/661723Wed, 26 May 2021 15:00:10 GMT