Reading Bytes from Serial

[muykim]

Is there a way to read a certain amount of bytes from the serial and type cast it into int or float? I've read through the QByteArray document, but I don't really get it.

[high_flyer]

Why not simply use QByteArray::toFloat() or toInt()?


I've read through the QByteArray document, but I don't really get it.
What exactly didn't you get?

[muykim]

I've tried using toFloat(), but kept on getting 0

[d_stranz]

You're going to have to show some code if you want help in finding what's wrong.

[muykim]

i.e.

QByteArray a("425AE78F");
float serial = a.toFloat();
qDebug() << serial;

I'm getting 0 instead of 54.72613. I don't think I'm doing it correctly.

[Lesiok]

This is example from QByteArray::toDouble doc :
QByteArray string("1234.56");
double a = string.toDouble(); // a == 1234.56Do you see the difference ?

[muykim]

Are you saying that the string a is not a float that's why it fails to convert?

[Lesiok]

Of course. The number of float type and its text representation is two different things. You must go back to the basics of C ++.

[muykim]

As you can tell, I'm still learning c++. If you don't mind, could you give me an example of how does the float conversion works?

"4h\xB2\xC9\xBC'\xB2\xC9<\xBC\xF9K;\xD1\xEB\x7F?"

The above is a chunk of my code, and I'm trying to convert it to float, but I couldn't get it to work. I really appreciate your help.

[Lesiok]

How is the data sent? The order of bytes is important.

[muykim]

Actually I'm reading the data from the serial. I have 9 values print out in arduino as double, so I want to read it 36 bytes at a time and convert it to float.

[Lesiok]

What does it mean "print out in arduino as double" ? You must do the opposite operation to "print out".

[d_stranz]

"4h\xB2\xC9\xBC'\xB2\xC9<\xBC\xF9K;\xD1\xEB\x7 F?"

Are these the actual bytes you get from the arduino, or have you converted them to a string? This could almost be an array of hexadecimal numbers except for all of the "punctuation / non-hex" characters in it.


QByteArray a("425AE78F");

And this is a hexadecimal number, represented as a string literal. You can't use the toDouble() or toFloat() conversions on such as string, because it doesn't represent the string form of a floating point number (ie. "1234.567").

You can convert this to a long or a long long using something like this:



QByteArray a("425AE78F");
long b = a.toLong( 0, 16 );

[muykim]

[QUOTE=d_stranz;301620]Are these the actual bytes you get from the arduino, or have you converted them to a string? This could almost be an array of hexadecimal numbers except for all of the "punctuation / non-hex" characters in it.

Yes, they are the actual bytes. This is kind of unrelated with the topic, but if I want to send a character 'a' to the serial, can I use serial -> write("a")?