Reading binary float data as string

Hi Folks,

I'm wondering whether I could achieve something like this from a
shell:
Suppose I do this from a C program:

MyFloatData = 3.513423;
fwrite(MyFloatData, sizeof(float), 1, pFile);

is there any  way to retrieve the string "3.513243" at the shell? I
would like to pass the string later on to bc or expr for processing.

Thanks
Jeenu

On 3 Apr., 13:36, Jeenu <jee...@gmail.com> wrote:
> Hi Folks,
>
> I'm wondering whether I could achieve something like this from a
> shell:
> Suppose I do this from a C program:
>
> MyFloatData =3D 3.513423;
> fwrite(MyFloatData, sizeof(float), 1, pFile);
>
> is there any =A0way to retrieve the string "3.513243" at the shell? I
> would like to pass the string later on to bc or expr for processing.

$ MyFloatData=3D3.513423
$ printf "%g\n" "$MyFloatData"
3.51342
$ printf "%s\n" "$MyFloatData * $MyFloatData" | bc
12.344141

Is that what you want?

>
> Thanks
> Jeenu

On Apr 3, 4:51 pm, Janis <janis_papanag...@hotmail.com> wrote:
> On 3 Apr., 13:36, Jeenu <jee...@gmail.com> wrote:
> 
> 
> 
> 
>
> $ MyFloatData=3.513423
> $ printf "%g\n" "$MyFloatData"
> 3.51342
> $ printf "%s\n" "$MyFloatData * $MyFloatData" | bc
> 12.344141
>
> Is that what you want?
>
>
> 

I'm afraid not. I wanted to read the binary data from file. Following
what you wrote:

MyFloatData=$(some_command_or_commands myfile) # MyFloatData should
now contain 3.513423

where "myfile" is to where the fwrite output went in OP.

On 4/3/2008 6:56 AM, Jeenu wrote:
> On Apr 3, 4:51 pm, Janis <janis_papanag...@hotmail.com> wrote:
> 
>
> I'm afraid not. I wanted to read the binary data from file. Following
> what you wrote:
>
> MyFloatData=$(some_command_or_commands myfile) # MyFloatData should
> now contain 3.513423
>
> where "myfile" is to where the fwrite output went in OP.

$ cat myfile
3.513423
$ awk '{print $1 "^2 = " $1 * $1}' myfile
3.513423^2 = 12.3441

Like that?

Ed.

On Apr 3, 5:05 pm, Ed Morton <mor...@lsupcaemnt.com> wrote:
> On 4/3/2008 6:56 AM, Jeenu wrote:
>
>
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
>
> $ cat myfile
> 3.513423
> $ awk '{print $1 "^2 = " $1 * $1}' myfile
> 3.513423^2 = 12.3441
>
> Like that?
>
>         Ed.

Still no :)

When I did fwrite in my C program, the file does no more contain the
string "3.513423", instead it's 4-byte (being of type float) *binary
data* - unlike fprintf. So `cat myfile` would give you only some non-
printable characters. My intention is to do something in shell, what
this would do in a C program:

fread(&MyFloatData, sizeof(float), 1, pFile);
sprintf(MyString, "%f", MyFloatData); /* MyString is of type char* */
printf("%s\n", MyString);

Here, program will print "3.513423"

Jeenu wrote:

> Still no :)
>
> When I did fwrite in my C program, the file does no more contain the
> string "3.513423", instead it's 4-byte (being of type float) *binary
> data* - unlike fprintf.

In other words, you want to read the IEEE (or similar) representation of a
float and convert it to a string, IIUC.
If everything else fails, you can always write a small program that fread()s
the data from the file and does a printf on stdout.

--
All the commands are tested with bash and GNU tools, so they may use
nonstandard features. I try to mention when something is nonstandard (if
I'm aware of that), but I may miss something. Corrections are welcome.

On Apr 3, 5:42 pm, pk <p...@pk.invalid> wrote:
> Jeenu wrote: 
> 
>
> In other words, you want to read the IEEE (or similar) representation of a
> float and convert it to a string, IIUC.
> If everything else fails, you can always write a small program that fread(
)s
> the data from the file and does a printf on stdout.
>
> --
> All the commands are tested with bash and GNU tools, so they may use
> nonstandard features. I try to mention when something is nonstandard (if
> I'm aware of that), but I may miss something. Corrections are welcome.

Yup, exactly. I could always use od or xxd to dump other binary data;
since float has a special bit encoding it's not possible ordinarily.
And yes, if nothing helps, I'll have to stick to my small program.