Converting hexadecimal string to floating point value

Question

I am reading data from an energy meter over modbus protocol and I am getting hex values from there. I want to convert that hex string to floating point value. For example - 0x416f0000 denotes a value of 14.9375.Reference

Can anyone please help me how to do it on Arduino IDE?

• Edgar Bonet: You mean Modbus ASCII, right? Non-ASCII Modbus doesn't use hex.

Answer 1

If you do indeed have an ASCII string of hexadecimal numbers (and not a raw binary float), then your best option may be to do the conversion in two steps:

1. convert the string to a 32 bit unsigned number using strtoul()
2. reinterpret the binary pattern of this integer as a float.

For example, the following program:

void setup() {
 const char modbus_data[] = "416F0000";
 union {
 uint32_t i;
 float f;
 } data;
 data.i = strtoul(modbus_data, NULL, 16);
 Serial.begin(9600);
 Serial.println(data.f, 4);
}
void loop(){}

prints 14.9375.

Note that for strtoul() to function properly, the hex string must be followed by a character that is not a valid hex digit (a 0円 in the example above).