Splitting a floating variable into 4 bytes?

Projects General Guidance
1

Hey all,

I am working on a project where I need to split a floating variable into 4 bytes so I can transfer them over a rs485 setup.

I have been able to do this with int variables by using highByte and loByte; then I am able to reconstructing them using Value = word(loValue, hiValue);

Is there a function that can do this for a floating type that can split it into 4 variables?

Any help would be much appreciated. Thank you.

Andrew

2

Make a union of a float with byte [4];

3

Check out unions:
union unpack {
float f;
byte b[4];
}

4

Btw, there is no guarantee that the receiving equipment uses the same representation for floats. Even if they both use IEEE954, there could be endian issues.

5

As mentioned, endiness etc. might be a problem.
So is the size of the float. It's usually 4 bytes, but not always.
I would do something like this:

char *pf = reinterpret_cast<char*>(&float_variable);
for (byte i = 0; i != sizeof(float); ++i)
     send_byte(*pf++);
6

You could always send the "string" number, not the binary float number.

7

Except we don't know what is on the other end of the RS485, which - by implication - is some older bit of machinery that requires who knows what to function.

8

Hey all,

First, i wanted to say the receiving end is another Arduino Mega.

So after reading the responses and a tad more googling am i on the right track with the below code?

void loop()
{
  float temperature = 1.32324;
  temperaturebytebreakout(temperature);
}

void temperaturebytebreakout(float f) 
  {
  byte * b = (byte *) &f;
  temperature0 = (b[0]);
  temperature1 = (b[1]);
  temperature2 = (b[2]);
  temperature3 = (b[3]);
  }

Now for the receiving side I am really lost on how to proceed in order to put the float back together.

Thanks for all your help thus far.

Andrew

9

See reply #2 - use a union.

To send you put the float in and take out 4 bytes. To receive you put in 4 bytes and take out a float.

10

A union would be cleaner and more portable.

11

Thanks everyone! I think I may have it working.

Andrew

12

I was going to say that the union helps protect against alignment issues, but I don't think that is a problem for the Arduino.