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I am trying to convert a float value to a 4-byte hexadecimal value.

For example my input is: 58.5. My expected output is: 426A0000 or like 0x42 0x6A 0x00 0x00.

My program is:

void setup() {
  Serial.begin(9600);
  float z = 128;
  unsigned i;
  unsigned char *chpt;
  chpt = (unsigned char *)&z;
  Serial.print("Float Value             : ");
  Serial.println(z);
  Serial.print("4 Byte hexadecimal Value: ");
  for (i = 0; i < sizeof(z); i++) {
    Serial.print(chpt[i],HEX);
    //Serial.print(" ");
  }
  Serial.println();
}
void loop() {
}

My current output is:

Float Value : 128.00

4 Byte hexadecimal Value: 00043

1

This value looks pretty correct to me. It is stored in little endian thou.

0x43000000 is the actual value.

Serial.print(x, HEX) truncates leading zeros. so 00 gets 0 So your output is 0 0 0 43 which corresponds to the little endian representation of the above.

Make yourself familiar with the floating point representation IEEE-754.

Also try the online FoatConverter.

Try the following:

char floatString[9];
sprintf(floatString, "%02X%02X%02x%02x", chpt[3], chpt[2], chpt[1], chpt[0]);
floatString[8] = '\0';
Serial.print(floatString);
| improve this answer | |
  • Thanks for the reply @kwasmich If I input the float value say Float Value : 235.56 I am getting values like this. 4 Byte hexadecimal Value: 5C8F6B43 Any changes in the program that you would like to suggest to obtain the result as 436B8F5C – Josh Earnest Dec 4 '19 at 8:14
  • I just added some sample code that should give you what you wanted in the first place. – Kwasmich Dec 4 '19 at 8:15
  • printf is a powerful tool. %02X means, print the value as hex (x) with at least 2 places width (2), padded with zeros(0). – Kwasmich Dec 4 '19 at 8:17
  • Thanks a lot!!!!!!!!!!!!! I as able to get my output. But then I am manually entering the float values. What should I change in the program so as to input a float value from Serial monitor and get the output in serial monitor? – Josh Earnest Dec 4 '19 at 8:27
  • I don't have a ready made solution for that. But the steps would be similar but in reverse. Use String string = Serial.readString(); to obtain the entire string in one block. Use sscanf(string.c_str, "%02X%02X%02X%02X", &chpt[3], &chpt[2], &chpt[1], &chpt[0]); to transfer the read hex values into the byte array. Something like that. – Kwasmich Dec 4 '19 at 8:33

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