Passing float values in FIFO

navderm · 01-02-2009, 08:25 AM

Hie Everyone,

I have been trying to pass the float values in FIFO but have not been able to do this. Probably because of some problems with the pointer.

Could you please help me do this.

Here is what I am trying to do:

I have two modules
1. Linux
2. RT Linux (i have started the function which allows the RT to use float point numbers)

Now
1st step : i transfer a float value from Linux to RT.
2nd step : i transfer the same value from RT to Linux.

The code should give me back the same no. in printing but it doesn't.

Any help would be greatly appreciated.

jim mcnamara · 01-02-2009, 11:38 AM

Are you passing IEEE-754 format float values or pointers? You cannot use pointers to reference the same memory location from two separate processes.

navderm · 01-03-2009, 08:21 PM

I do not think that is correct. I have sorted out the problem
The point is the computer cannot know whether the pointer is for a float or not unless it is told the same. So if i am supposed to pass a character pointer, it considers any pointer as character pointer. Hence if i first pass a float pointer with a typecast of character. i accepts. Now if i convert the same pointer (or say accept this pointer) in other program with a float type cast, it works fine. I have the code, if you need it,jim.

thx

ta0kira · 01-04-2009, 03:00 PM

Code:

float my_value = 0.0;

//...

write(fd, &my_value, sizeof my_value);

//...

read(fd, &my_value, sizeof my_value);

That really isn't a good idea unless you know this will always happen on the same machine, so normally I convert numbers to text before sending them. There normally isn't much of a point sending values in their binary formats unless you're sending precisely-aligned data structures with exacting binary information; a category that floating points don't fall into. You won't lose much converting to and from a string with *printf and strto*. And unless you're sending strictly a single type and nothing else, you'll need some sort of alignment control (which is usually done with a simple text protocol) to prevent a minor error from corrupting all subsequent IPC.
ta0kira