identifier qrand is undefined

Roberrt

Im trying to update this project: https://github.com/omkar-developer/QtCaptcha

But when i replace rand to QRandomGenerator::global() i get many compile errors

JonB

@Roberrt Always look at the first error.

Chris Kawa

@Roberrt Please please read that page I linked. It's the least you can do.
QRandomGenerator::global() returns an instance of the generator. To get a number call
QRandomGenerator::global()->generate()

Roberrt

@Chris-Kawa said in identifier qrand is undefined:

QRandomGenerator::global()->generate()

Im already using QRandomGenerator::global()->generate() it was just a typo

Chris Kawa

@Roberrt Then what's the error?

Roberrt

@Chris-Kawa i've been able to fix some, but this one don't:

https://github.com/omkar-developer/QtCaptcha/blob/6356446e4864bcb7acfd332165f0073a247c71a0/captcha.cpp#L455

text += chars[(qrand() / (qreal) RAND_MAX) * (chars.size() - 1.0)];

to

text += chars[(QRandomGenerator::global()->generate() / (qreal) RAND_MAX) * (chars.size() - 1.0)];

Now im getting this error: no operator "+=" matches these operands

I don't know if replacing these rands messed something up in the code, I'm getting a different layout than in her GitHub pictures

probably I shouldn't remove this line as @JonB suggested

void Captcha::randomize()
{
    //qsrand(QTime::currentTime().msec());
}

JonB

@Roberrt
qsrand() seeds for qrand(). It has nothing to do with QRandomGenerator.

RAND_MAX is also for qrand(). Just casting it to qreal does not mean it's suitable to use with QRandomGenerator.

Why are you indexing an array by a qreal expression?

Roberrt

@JonB This project is not mine, im just trying to use it, but got these qrand errors

Chris Kawa

This expression (qrand() / (qreal) RAND_MAX) gives you a random double number in range 0..1.
So you can just replace this whole thing with QRandomGenerator::global()->generateDouble(), which does the same. Same for the lines above it.
Or better yet - remove that whole expression with bounded() which will give you a random index in a range and you won't have to do any of those shenanigans.

Now im getting this error: no operator "+=" matches these operands

text is a QString. chars[x] is an unsigned char. Convert it to QChar. Also convert the expression in [] to an integer.

probably I shouldn't remove this line as @JonB suggested

If there's a function that seeds the generator and you want to preserve it then you can use QRandomGenerator::seed, but it's not necessary.

Roberrt

@Chris-Kawa thanks, changing it to QRandomGenerator::global()->generateDouble() fixed the widget not being show correctly.

text += QChar(chars[(QRandomGenerator::global()->generate() / (qreal) RAND_MAX)  * (chars.size() - 1.0)]);

I'm getting an exception index out out of range

Chris Kawa

@Roberrt said in identifier qrand is undefined:

(QRandomGenerator::global()->generate() / (qreal) RAND_MAX) * (chars.size() - 1.0)

Replace this whole thing with

QRandomGenerator::global()->bounded(chars.size())