错误的有效载荷转换 Arduino

Question

Hello I'm newbie with arduino and maybe is a silly question, but I'm trying to convert long numbers to byte .

My code is:

float f_longitud = 179.1234567;
byte payload[4];

long longitud= f_longitud * 10000000;
SerialUSB.println(longitud);

payload[0] = (byte) ((longitud & 0xFF000000) >> 24 );
payload[1] = (byte) ((longitud & 0x00FF0000) >> 16 );
payload[2] = (byte) ((longitud & 0x0000FF00) >> 8 );
payload[3] = (byte) ((longitud & 0X000000FF));
SerialUSB.println(payload[0]);

The problem is that the first println theoretically has to show 1791234567 , because I'm just multiplying 179.1234567 x 10000000 but it shows 1791234560 . Why is this 0 appearing? Where is the 7?

The second problem is that payload[0] should be 6A hex, but my println shows 106 . Why is not converting it correctly? Does this problem comes because of the previous error?

Below I show a scheme of what I'm doing. It's from the this link .

Thank you very much!

Answer 1

The problem is that the first println theoretically has to show 1791234567, because I'm just multiplying 179.1234567 x 10000000 but it shows 1791234560. Why is this 0 appearing? Where is the 7?

This is probably due to precision limits of float . Try double instead.

The second problem is that payload[0] should be 6A hex, but my println shows 106.

You can provide a format for println() , like this:

SerialUSB.println(payload[0], HEX);