How to write ULONG into QVariant ?

[SPlatten]

I have a 'ulong' with the value '18446744073709551615', this is the absolute maximum value.

I can see in the debugger that a QVariant has the correct value stored:

1.8446744073709552e+19

I try to copy this from the variable into a type of ulong:

ulong ulngCheck;
memcpy(&ulngCheck, varCheck.data(), sizeof(ulngCheck));
blnPass = ((ulngCheck - ulngData) == 0);

ulngData is another ulong which does have the value:

18446744073709551615

When I single step in the debugger over the memcpy operation, ulngCheck has the value:

4895412794951729152

Why ?

[SGaist]

Hi,

Using:

ulong ulngCheck = varCheck.value<ulong>();

would likely be simpler.

[edit: fixed type SGaist]

[SPlatten]

@SGaist said in How to write ULONG into QVariant ?:

long

Thanks, slight alteration:

ulong ulngCheck = varCheck.value<ulong>();

There are a few types where this method fails, these are: char, uchar and ulong, in the case of char and uchar using:

char uValue = varCheck.value<char>();

or

uchar ucValue = varCheck.value<uchar>();

The returned value is 0, yet in the debugger varCheck contains 'a'.

ulong ulngValue = varCheck.value<ulong>();

varCheck contains: 1.8446744073709552e+19
Yet, ulngValue is converted to: 9223372036854775808
So the result still isn't correct.

The only way I found of getting the correct value back out of varCheck when it is assigned a ulong is:

double dblCheck = varCheck.value<double>();

This then extracts: 1.8446744073709552e+19.

[Christian Ehrlicher]

Provide some code instead pretty printed output from the debugger:

int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  qulonglong ql = 18446744073709551615ULL;
  uint64_t ui = ql;
  unsigned long ul1 = ql;
  ulong ul2 = ql;
  qDebug() << sizeof(ql) << sizeof(ui) << sizeof(ul1) << sizeof(ul2);
  qDebug() << ql << ui << ul1 << ul2;
  QVariant v1(ql);
  ulong out = v1.value<ulong>();
  qDebug() << out;
}

-->
8 8 8 8
18446744073709551615 18446744073709551615 18446744073709551615 18446744073709551615
18446744073709551615

[SPlatten]

@Christian-Ehrlicher, does your example produce the same result with:

 ulong ul2 = 18446744073709551615;
 QVariant v1(ul2);

?

[Christian Ehrlicher]

@SPlatten said in How to write ULONG into QVariant ?:

does your example produce the same result with:

So hard to try it by yourself? Your compiler should inform you about what you're doing wrong btw...

/edit: http://www.cplusplus.com/doc/tutorial/constants/
"These literal constants have a type, just like variables. By default, integer literals are of type int. "