How to convert byte array to float

Question

How can I convert a byte array to float?

Code:

void send_data() {
    CCPACKET data;
    data.length=2;

    float lon=26.533255;
    float lat=27.533463;


    data.data[0]=lon;
    data.data[1]=lat;

    if(cc1101.sendData(data)){
    Serial.println(data.data[0]);
    Serial.println(data.data[1]);

    Serial.println(" sent ok ");
    return true;
    }else{
    Serial.println("sent failed ");
    return false;
    }

 }

The problem is when I print those two variables it just prints lon 26.00 and lat 27.00 but not lon 26.533255 lat 27.533463 as I expected.

Here is the header file for CCPACKET I use:

#ifndef _CCPACKET_H
#define _CCPACKET_H

#include "Arduino.h"

/**
 * Buffer and data lengths
 */
#define CC1101_BUFFER_LEN        64
#define CC1101_DATA_LEN          CC1101_BUFFER_LEN - 3

/**
 * Class: CCPACKET
 * 
 * Description:
 * CC1101 data packet class
 */
class CCPACKET
{
  public:
    /**
     * Data length
     */
    byte length;

    /**
     * Data buffer
     */
    byte data[CC1101_DATA_LEN];

    /**
     * CRC OK flag
     */
    boolean crc_ok;

    /**
     * Received Strength Signal Indication
     */
    byte rssi;

    /**
     * Link Quality Index
     */
    byte lqi;
};

#endif

I was trying to fix it by this part of code, but without success:

float lon=26.533543;

*((float *)data.data[0]) = lon;

Can someone help me to convert the byte array to float?

Answer 1

You can choose to treat the byte array as a float array by typecasting. Your attempt isn't far from a solution:

((float *)data.data)[0] = lon; // uses data.data[0] ... data.data[3]
((float *)data.data)[1] = lat; // uses data.data[4] ... data.data[7]

When printing you should also treat the data array as float array:

Serial.println(((float *)data.data)[0]);

It looks like you are sending the data over some interface. Then of course you need to typecast the binary data back into a float at the receiving end (if you want to do something useful with it) - similar to what is done above when it is passed to Serial.println.

Answer 2

/** Data buffer/ byte data[CC1101_DATA_LEN];

That line of code declares an array of datatype byte. I suggest you review variable declaration for Arduino.

A byte will store an 8-bit unsigned number with a range of 0 to 255, no decimal points. I also suggest you review truncation to understand how computer systems handle mathematic calculations that produce decimal results when the result is being stored in a variable type that doesn't store decimals.

A float stores a 32-bit value with decimal point.

The quick answer to your problem is to change the above quoted code from byte to float.