reading back a float number

Question

I am using microchip c18 and i have this function which splits the float in to 4 respective bytes.And C18 follow little endianess

a[0]=*(fptr);        address 0
a[1]=*(fptr+1);              1  
a[2]=*(fptr+2);              2    
a[3]=*(fptr+3);              3

and writes in to serial eeprom.

If i wanted to read back the float variable.

float read_float(void)
{   float f;
    unsigned char *fptr;
    fptr=&f;

    *(fptr)=eepromread(0);
    *(fptr+1)=eepromread(1);
    *(fptr+2)=eepromread(2);
    *(fptr+3)=eepromread(3);      

    return(f);       
}

Will this function return the float variable?. I'm devoid of any hardware and simulation tools right now.

I trust I'm clear on my question. edit:

While doing so. a compiler mismatch error occurs on assigning char to float..How could i remove the error?

oops.Thank you @suspectus.Newbie here.So *(fptr) is the correct way right — Rookie91, Mar 24 '14 at 09:33
it wouldn't be difficult to write a unit test for this by mocking eepromread — Vorsprung, Mar 24 '14 at 09:34
Type mismatch error do occurs while doing so.I think assigning 'char' *fptr to 'float' &f has been a problem and compiler does invokes an error signal — Rookie91, Mar 24 '14 at 11:27
`*(fptr+2)` and `*fptr+2` are very different things, decide which one you want and stick to it — M.M, Apr 03 '14 at 09:22

John C · Answer 1 · 2014-03-24T12:38:42.220

1

The cleanest way is *(char*)(fptr+i) = eepromread(i);. You want the offset from the initial pointer, cast to a pointer to a character, dereferenced.

Also, at least my compiler (gcc) balks at that first assignment. You need something more like fptr = (char*)(&f); so that the pointer to the float is assignment-compatible.

Double-check, though, to be sure that eepromread() gives you the bytes in the order that you expect them. They should, since IEEE754 is independent of byte-ordering, but the number of "clever enhancements" hidden in embedded C libraries could fill a pretty big book.

edited Mar 24 '14 at 12:38

answered Mar 24 '14 at 12:14

John C

1,931
1
22
34

`fptr` is `unsigned char *`, I don't see what you gain by casting it to `char *` – M.M Apr 03 '14 at 09:23

reading back a float number

1 Answers1