Reading double Value PIC18F67K22

Question

char q[150];
void main(void){

System_Initialization();
UART_Init_2();

 while(1){ 

 double A=23.045610;
 sprintf(q,"%f\r\n",A);    
 UART_Tx_2(q);}}

When I Read value of A its give 23.045410 instead of 23.045610 anyone know why this will happened? i am using PIC18F67k22 controller and Xc8 Compiler

https://stackoverflow.com/questions/588004/is-floating-point-math-broken — Yunnosch, Mar 19 '18 at 07:24
Why are you using floating point on a lousy PIC with no FPU? — Lundin, Mar 19 '18 at 07:31
@Lundin, I think you were too hasty closing this question. The surprising behaviour here is that you get so few digits of precision with doubles. — Thomas Padron-McCarthy, Mar 19 '18 at 07:33
@ThomasPadron-McCarthy Feel free to find a better duplicate. These kind of questions have been asked thousands of times before. — Lundin, Mar 19 '18 at 07:35
@lundin The dupes are indeed wrong, as it's related to a compiler setting of the pic chip (which defaults to 32bit doubles) — Lanting, Mar 19 '18 at 08:00
Did find the right dupe btw: https://stackoverflow.com/questions/22412584/rounding-issue-when-using-long-long-on-pic — Lanting, Mar 19 '18 at 08:01

score 2 · Answer 1 · answered Mar 19 '18 at 07:32

2

On the PIC18, the data types float and double are the same, and only 32 bits long. That is not enough bits to store more than five or so decimal digits. Therefore you can expect some rounding error at the end of the decimals.

answered Mar 19 '18 at 07:32

Thomas Padron-McCarthy

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Reading double Value PIC18F67K22

1 Answers1