From: 1gor <idrozdov@...>
Date: 2006-07-10T01:50:05+09:00
Subject: Ruby C extension/wrapper around  C function that uses scanf and printf

I need  Ruby to access a set of external command line applications for
dataseries analysis. Each of these little apps simply reads data from
stdin and then outputs processed results to stdout (using scanf and
printf, they are all written in C).

These functions have to be accessed repeatedly when iterating over
large chunks of data, so accessing them through the pipe (popen or
popen3) doesn't work. Launching/closing an external process 3000 times
in a row results in errors. And that's not efficient. So I have to
write extension for each of those little C programs, a wrapper of
sorts.

I have learned how to write and compile an extension for Ruby. I can
import an extension, pass an array of data to it and return some data
from the extension. The problem is that I have no C experience and
dread thinking of having to replace each 'scanf' routine with my custom
array of imported data (memory allocation, writing iterator etc.). Each
input function here starts with:

     while (scanf("%lf", &y) == 1) { ... etc.

and then follows to process input data, handle cases with input buffer
is too large etc. I would very much like to leave these input()
functions as they are and just feed them my data from Ruby code.

Is it possible to fill stdin buffer with data from Ruby code and then
simply call existing C function that uses 'scanf'? I couldn't simply
assign an array to $stdin variable in Ruby, gave TypeError (File
expected)...