[Interest] String best practice

[Ch'Gans]

On 14 March 2017 at 22:43, Harald Vistnes <harald.vistnes at gmail.com> wrote:
> Hi,
>
> I'm currently working on reading and parsing large ASCII based text files
> and I am wondering what is the current best practice. There are so many
> classes and macros available, so it can be a bit confusing to know what to
> use when.

Can you define 'large', eg, 1MG, 1GB or 1TB?

>
> QString, QLatin1String, QByteArray, QStringLiteral, QLatin1Literal,
> QByteArrayLiteral, plain C++ string literal, QStringRef, QStringBuilder and
> so on. And then std::string and raw const char* strings.
>
> In my case I want to read a large ASCII file line by line, so I don't need
> unicode. I need to compare a string with a literal, extract substrings and
> convert some strings to numbers.

If you use QIODevice, you'll get data as QByteArray, which can be used
for basic comparison, splitting, searching, substring extraction and
to/from numbers.

>
> Should I just use QString all the way, or is it faster to use some other
> classes when you know you don't need unicode?
>
> Any hints on fast file parsing code in Qt itself that I could use as a
> guildeline?

I once used QRegularExpression for parsing text file that had a
'headache' file format, i was surprise by the velocity of the result,
at least i was good enough for me. I mean certainly slower than plain
C code using char*, but the code was so much easier to write, read and
test.

Chris

>
> Thanks,
> Harald
>
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