QString/C++ convert to number

SGaist

See, you have strings coming from three different sources so not so a strange question ;-)

As for your issue, if you have a set of methods that do exactly what you want then go on and use them if they have no equivalent in a Qt. There's nothing wrong with using the stdlib if it has what you need.

JonB

@SGaist
That's OK, you usually answer my question with a question ;-)

At the time I raised the question, I had not thought of atol and I didn't know it was in stdlib in C++. So you are saying that's OK for me in 2020? If I get shouted at elsewhere I may quote you on this?

JonB

@kshegunov said in QString/C++ convert to number:

I'd just go with a pre-prepared regex as it's easiest to use and quite straightforward.

Speechless. I do not want to use a regular expression to parse a string when all I want is a function to read some digits, like QString::toInt(). I am shocked that you are prepared to advocate this. We're not going to agree.

Are you also OK with me using atol(), if there's nothing more appropriate? Which I had thought there would be.

kshegunov

@JonB said in QString/C++ convert to number:

We're not going to agree.

Like this is something new ...

Are you also OK with me using atol(), if there's nothing more appropriate?

Absolutely.

aha_1980

Hi @JonB,

I know that problem, and therefore I created QTBUG-66115. You might want to comment and vote there ;) Till a resolution is done, using a regexp might be the simplest thing to use.

Regards

JonB

@aha_1980
Ah ha! A kindred spirit, who recognises this limitation in the QString::toInt() etc. methods. FWIW I have appended my comment into the bug request.

I should rather burn in Hell than resort to a regular expression to solve this! I shall change to using the stdlib atoi() or strtol() now. Might as well have stuck to C as ever move to C++... ;-)

aha_1980

Hi @JonB,

Might as well have stuck to C as ever move to C++... ;-)

Nah, C is not that bad, and atol is hard to misuse (at least harder than scanf...).

The only problem is, that you have to convert your QString toLatin1() first.

Regards

JonB

@aha_1980

convert your QString toLatin1() first

Fortunately, I don't. I speak Latin, and I only need to support other Latin speakers, you don't speak Latin then you lose... :)

EDIT OIC, I was wrong about this, see next post below!

kshegunov

@JonB said in QString/C++ convert to number:

Fortunately, I don't. I speak Latin, and I only need to support other Latin speakers, you don't speak Latin then you lose... :)

The problem, as usual, is the locales, where each country has its twisted way of writing numbers - decimal separators and such. Hence André's humongous patch. :)

JonB

@aha_1980 said in QString/C++ convert to number:

The only problem is, that you have to convert your QString toLatin1() first.

OIC, I was wrong about this. I assumed that given that QString accepts const char * in a constructor it would have an implicit "to const char *" conversion operator. Damn these multiple languages... :)

I suspect I've asked this before, but: you recommend QString toLatin1(), but in docs I read:

You can also pass string literals to functions that take QStrings as arguments, invoking the QString(const char *) constructor. Similarly, you can pass a QString to a function that takes a const char * argument using the qPrintable() macro which returns the given QString as a const char *. This is equivalent to calling <QString>.toLocal8Bit().constData().

So I plan to use qPrintable(), i.e. QString::toLocal8Bit().constData() rather than your toLatin1()?

Kent-Dorfman

it's a bit heavy weight but I always like a good RE engine for parsing most things.

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