converting QByteArray to unsigned short

[sattu]

sattu,

Why not use QVector<quint16>? What is it you are trying to accomplish?

hi Timotoe,
Actually i'm passing some data from server to client. And data passing is possible only through qbytearray or char* way. But the crc of data that i'm calculating is of unsigned short type. But ultimately i have to pass it along with data. That's why i asked this question. So can you suggest me any way?

[tbscope]

Dudes... really...

QString::number(ushortNumber, 16)

QString::number(ushortNumber, 16)

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:-)

[wysota]

This will make it a string ("2CEC") and not a value ("\x2C\xEC"). I don't know if that's expected but if so then the question was not asked very precisely.

[sattu]

This will make it a string ("2CEC") and not a value ("\x2C\xEC"). I don't know if that's expected but if so then the question was not asked very precisely.

Hi wysota!
You are right, actually i wanted value, not string. But that's not a problem, in the code that tbscope gave, i used QByteArray instead of QString and it is working fine. But the only issue is of memory.

[wysota]

But that's not a problem, in the code that tbscope gave, i used QByteArray instead of QString and it is working fine. But the only issue is of memory.

You are wrong. The code stores it as a string and not as a value, that's why it's taking four bytes ('2', 'C', 'E', 'C') and not two. The method I gave you should be working fine, maybe you just check it wrong. The code I gave you works just fine.

#include <QtDebug>
#include <QByteArray>
 
int main(){
  unsigned short val = 0x2CEC;
  QByteArray ba((const char*)&val, sizeof(val));
  qDebug() << "size:" << ba.size();
  qDebug() << "hexdump:" << ba.toHex();
  return 0;
}

#include <QtDebug>
#include <QByteArray>

int main(){
  unsigned short val = 0x2CEC;
  QByteArray ba((const char*)&val, sizeof(val));
  qDebug() << "size:" << ba.size();
  qDebug() << "hexdump:" << ba.toHex();
  return 0;
}

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yields:

$ ./ba 
size: 2 
hexdump: "ec2c"

$ ./ba 
size: 2 
hexdump: "ec2c"

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Note the byte order is reversed (my machine is little endian), hence the unportability I mentioned!

[sattu]

You are wrong. The code stores it as a string and not as a value, that's why

#include <QtDebug>
#include <QByteArray>
int main(){
  unsigned short val = 0x2CEC;
  QByteArray ba((const char*)&val, sizeof(val));
  qDebug() << "size:" << ba.size();
  qDebug() << "hexdump:" << ba.toHex();
  return 0;
}

#include <QtDebug>
#include <QByteArray>
int main(){
  unsigned short val = 0x2CEC;
  QByteArray ba((const char*)&val, sizeof(val));
  qDebug() << "size:" << ba.size();
  qDebug() << "hexdump:" << ba.toHex();
  return 0;
}

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!

Oh yes, you are right. Actually i had checked it wrongly in the locals and watchers section. It is working as you have told. Well exactly speaking even the reverse order is not a problem. we have to send it from the server side in a qbytearray, that's it. But now the problem is how to convert it back to ushort(in the client side)? I have tried it with .toUShort, but it's not working, as the crc is in hexadecimal form. Let me see, if it's possible, otherwise i will have to trouble you again.

many many thanks for helping me,

With regards,

[tbscope]

ushort theNewShort = 0;
memcpy(&theNewShort, ba.data(), sizeof(ushort));

ushort theNewShort = 0;
memcpy(&theNewShort, ba.data(), sizeof(ushort));

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Conditions: the bytearray contains only those two bytes.

[sattu]

ushort theNewShort = 0;
memcpy(&theNewShort, ba.data(), sizeof(ushort));

ushort theNewShort = 0;
memcpy(&theNewShort, ba.data(), sizeof(ushort));

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Conditions: the bytearray contains only those two bytes.

Thanks tbscope, it's working great. i'm able to do both type of conversion.
but if i use this code to put an ushort into a qbytearray: QByteArray::number(crc, 16); as you had suggested earlier, then how to retrieve back the ushort from the qbytearray again?

[wysota]

In this situation you can use QByteArray::toUShort() with 16 as the base.

[sattu]

Dudes... really...

QString::number(ushortNumber, 16)

QString::number(ushortNumber, 16)

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:-)

Thanks a lot tbscope for this post.
It's working fine. But well, one more question. here i have taken crc=11500(2cec in hex). Here 2C is one byte and EC is another byte. But when i'm storing it in a QByteArray using the code you gave, it is taking 4 bytes instead of 2 bytes. I mean to say it is storing 2,C,E,C in 4 separate boxes(bytes). Now, it is working fine. But is there any way to put this data inside 2bytes of array rather then 4 bytes(which it is normally taking). Sorry to disturb you, but i would be much thankful if you could help me.


With regards,

[tbscope]

it is taking 4 bytes instead of 2 bytes.

I missunderstood. Just ignore my post.