[Interest] string conversion to longlong error

[Rogers Nate]

On 09/03/2014 11:53 AM, Calogero Mauceri wrote:
> Hi all,
>
> I'm doing something really simple, but which is driving me crazy.
>
> I'm reading a string from a file and converting it to a long long 
> integer, but the conversion fails.
> The code I'm running is as simple as this
>
>      // this string is read from a file
>      QString str("18446744073709551615");
>      bool ok;
>      qint64 value = str.toLongLong(&ok);    // Error
>
> the number should be representable in 64 bit. Am I doing something wrong?
>
> More hints, if I convert the number to unsigned long long integer then 
> it works
>
>       bool ok;
>       quint64 value = str.toULongLong(&ok);    // OK
>
> Similarly initializing the long long from the literal value is failing too
>
> Q_INT64_C(18446744073709551615) ;      // Error, returns -1
> Q_UINT64_C(18446744073709551615);    // OK
>
> Thanks for your help!
>      Calogero
>

18446744073709551615 is too big to fit into a long long.  It is actually the biggest number you can have a unsigned long long.  A long long can't fit the same size number because it has to use one bit to hold the sign.  The maximum number you can fit in a long long is 9223372036854775807.

Nate



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