CODEWITHSUNDEEP
cruby
Nicolas Sounac
Nicolas Sounac

Reputation: 91

Trying to call C program from Ruby script

I am trying to call a C program from my Ruby script, parsing it an argument (file object) and then store some variables the C program would return.

The idea is that my Ruby script allows me to easily cycle through the files & folders of a parent folder but it is way too slow to efficiently process all the files in that folder. Hence the use of a C program that I want to call to process each file.

My problem is that I can't find a method to call that C program from Ruby (and how to parse it the file argument, I'm not even sure it is possible as I don't know if Ruby files objects and C streams are "compatible")

Thank you in advance for your help !

Upvotes: 1

Views: 694

Answers (2)

user240438
user240438

Reputation:

One simple traditional way for a Ruby process to interact with unrelated C code is popen, which will allow your Ruby process to invoke the (compiled) code as a separate process, passing your choice of arguments into the traditional space the operating system allocates for that (accessible in argv in your process's int main(int argc, char** argv)), and then interacting with its standard input and standard output over a pipe. However, this technique launches another process and requires that you serialize/deserialize any ongoing interprocess communication so that it can run over the pipe, which may be an impediment.

So you can also write the C code as a Ruby extension, which will allow you to return values more readily, and moreover avoids the overhead associated with having a separate process involved. However, note that if you perform extensive work with Ruby objects in your C code you may still incur the performance penalties you'd hoped to avoid. The canonical document on how to write Ruby extensions is README.EXT.

Upvotes: 1

Darren Stone
Darren Stone

Reputation: 2068

You say you are trying to call a program so I assume you are not trying to statically or dynamically load a library and call a function. (If you are trying to load a library to call a function then look to the DL::Importer module.)

As for calling an external program from Ruby and receiving its result (from stdout, in this case), regardless of whether it was written in C or not, an easy way to do it is:

value = `program arg1 arg2 ...`

e.g. if the program you want to call compresses a given file and outputs the compressed size. 

size = `mycompressionprogram filename.txt`
puts "compressed result is: #{size}"

Note those are back ticks " ` ".

So this is one easy way to code your computationally heavy stuff in C and wrap it up in a Ruby script.

Upvotes: 2

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