CODEWITHSUNDEEP
c++qtqt5
Mark
Mark

Reputation: 5102

Qt5: toLongLong fails

I'm trying to convert a QByteArray that contains a value in hex format to long long:

QByteArray field = "A8BC301F0193E83F";
bool ok;
qlonglong val = field.toLongLong(&ok, 16);
qDebug() << ok << val;

output:

false 0

Instead I'm expecting val = -6.288.098.069.987.465.153.

Why it fails? The docs says nothing about any limitation of this function.

I forgot to mention the data order is little endian in the source.

Upvotes: 1

Views: 489

Answers (2)

pat
pat

Reputation: 497

You can find the final function Qt call to convert ByteArray to long long here qlocale.cpp in function static qlonglong qstrtoll

It defines cutoff = neg ? qulonglong(0-(LLONG_MIN + LLONG_MAX)) + LLONG_MAX : LLONG_MAX;.

So cutoff will be 0x8000000000000000 if neg, or will be 0x7fffffffffffffff if non neg.

Your input value is bigger than cutoff so it returns false.

You can get the static qlonglong qstrtoll function and debug by your own.

Upvotes: 1

cbuchart
cbuchart

Reputation: 11575

Your number exceeds the limits of a signed long long, so conversion fails.

You can use QByteArray::toULongLong instead and then make a cast to long long.

#include <qbytearray.h>
#include <qdebug.h>

int main(int argc, char* argv[])
{
  QByteArray field = "A8BC301F0193E83F";
  bool ok;
  qlonglong val = field.toLongLong(&ok, 16);
  qDebug() << ok << val;

  qulonglongval_u = field.toULongLong(&ok, 16);
  qDebug() << ok << val_u << (long long)val_u;

  long long check = 0xA8BC301F0193E83F;
  qDebug() << check;

  return 0;
}

EDIT: you can take a look at the source code of the associated helper function and see that this is indeed the case between signed and unsigned integers.

Upvotes: 2

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