Re: [example] how to get popen2() working? [XP, MSVC 2.9.15-octave]

[Muthiah Annamalai]

andreas.naessl wrote:
> hi all,
>
> i try to establish a simple bidirectional pipe-connection between octave and 
> a little "server"-programm written in python, for direct data-transfer without
> producing temp-file-trash; i thought of using octave's popen2(). the server 
> should be running continuously in the background, waiting for requests.
>
> but i cannot get it working really.
>
> [my System: win XP + Michaels MSVC-octave 2.9.15] 
>
> first: if i communitcate to my "server" directly at octave-prompt, 
> i get something back
> (although i don't understand the need of the fclear(b) command 
> when i want a second readline back from my server-app.) 
> please see octave-commandline-output below:
>
>   octave.exe:35> [a,b,i]=popen2('python','svr_02.py')
>   a =  8
>   b =  7
>   i =  20204
>   octave.exe:36> fputs(a,"test_command_at promt\n")
>   ans = 0  
>   octave.exe:37> fgets(b)
>   ans = got command  test_command_at promt    ### ok
>  
>   octave.exe:38> fputs(a,"0\n")
>   ans = 0
>   octave.exe:39> fgets(b)
>   ans = -1                        ### why this ? ###
>   octave.exe:40> fclear(b)
>   octave.exe:41> fgets(b)
>   ans = got command  0           ### ok
>
>   octave.exe:42> fclose(a)
>   ans = 0
>   octave.exe:43> fclose(b)
>   ans = 0
>
> second: if i put the same commands into a m-file (octave_cli.m),
> i don't get back anything to read. why this?
>
> code of "octave_cli.m":
>   [a,b,i]=popen2('python','svr_02.py')
>   # [a,b,i]=popen2('python',['-u','svr_02.py']) # unbuffered python doesn't work 
>   fputs(a,"testcommand\n")
>   fgets(b)
>   fputs(a,"0\n")  
>   # fgets(b)   gives on prompt here: ans = -1, so ...
>   fclear(b)
>   fgets(b)    # ...after fclear: ans = got command  0, but only on prompt 
> directly
>   fclose(a)
>   fclose(b)
>
> gives the output:
>   octave.exe:34> octave_cli
>   a =  9
>   b =  8
>   i =  20360
>   ans = 0
>   ans = -1    # here i should get back my sent command-string
>   ans = 0
>   ans = -1    # here also 
>   ans = 0
>   ans = 0
>
> third - just to be complete and going a bit octave-off-topic:
> the code the pythonic testing-server "svr_02.py"
> is added below. does anybody see a problem there?  
> with a python-client-connection i managed it working.
>
>   import sys
>   # little test-server-app., just echo-ing incoming commands
>   # command "0" terminates server
>   def main():
>     for line in iter(sys.stdin.readline,""):
>       ln = line
>       print "got command ", ln.rstrip('\n')   # answer-echo on stdout; remove 
> newline
>       # later insert data-transfer here
>       if ln == "0\n":
>         print ln, "exit.."
>         sys.exit(0)
>       sys.stdout.flush()     # important 
>       sys.stdin.flush()           
>   if __name__ == "__main__":
>     main()
>
> sorry for the long msg... the prob might be just a stupid mistake by me, 
> as i'm not really a programming-expert...
> anyway, i would strongly appreciate any hints by the community
>
> thanks, best regards
> andreas
My message is not directly related to solving your problem.
I think tk_octave package by Paul Kienzle, from octave-forge does
something like this; just between tk and octave using sockets.
Maybe you want to look at that source code.

-Muthu