What to pass to QSqlQuery::prepare() other than const char *

[l3u_]

Hi :-)

I have QT_NO_CAST_FROM_ASCII set and use a lot of SQLite queries in my project. I wonder what's the best choice to pass the defined SQL queries to QSqlQuery::prepare() (sorry if this is a dumb question, I read the docs but I'm not sure if I fully understand them).

Should one use const QString::fromUtf8("SOME QUERY"), QLatin1String("SOME QUERY") or QStringLiteral("SOME QUERY")?

Thanks for all clarification/explanation!

Cheers, Tobias

[VRonin]

This applies to all methods taking a QString, not just QSqlQuery::prepare()

• Most of the cases: QStringLiteral("foo") if it will actually be converted to QString
• QLatin1String("foo") if it is use with a function that has an overload for QLatin1String. (such as operator==, operator+, startWith, replace, ...)

Source https://woboq.com/blog/qstringliteral.html

[l3u_]

@VRonin So … one should generally use QLatin1String wherever one defines an immutable string?

[VRonin]

@l3u_
No.
use QStringLiteral("foo") to generate an immutable QString, use QLatin1String only in methods that explicitly have a QLatin1String overload

Note that I said [immutable QString], not [immutable string]. For example, you still must pass a raw const char* to QObject::tr

[l3u_]

@VRonin Okay. So for the above case of QSqlQuery::prepare(const QString &), the QStringLiteral is the right choice, yes? I also read (at least a part of) that blog post you cited, but I still didn't know when to use what ;-)

[JonB]

@l3u_

So for the above case of QSqlQuery::prepare(const QString &), the QStringLiteral is the right choice, yes?

Yes!

What @VRonin (and the docs) is saying is:

• If the signature is const QString & then use QStringLiteral.
• Only if the signature is QLatin1String then use QLatin1String . (I imagine this will not be that many cases.)

[l3u_]

@JonB Thanks for the clarification. The docs are somewhat confusing ("It's better, but beware, it's not better for all cases") …