From: Charles Mills <cmills@...>
Date: 2005-04-05T04:29:43+09:00
Subject: Re: Extension question


Joe Van Dyk wrote:
> On Apr 4, 2005 8:34 AM, Charles Mills <cmills@freeshell.org> wrote:
> >
> > > Are there any general rules of thumb that you use when writing
> > extensions?
> >
> > http://www.ruby-talk.org/cgi-bin/scat.rb/ruby/ruby-talk/47700
> >
> > You shouldn't be able to cause your extension to seg fault from
Ruby.
> > That may sound like a joke, but I just mean using StringValue,
> > NUM2LONG, etc before you starting using Ruby objects in C.
>
> How should errors be handled in C extensions?  For example, my C
> extension was expecting a Ruby string, but it was passed an IO
object.
>

static VALUE
expecting_a_string(VALUE self, VALUE str)
{
  StringValue(str);
  /* str is now definately a String so I can
   * use RSTRING(str)->ptr, RSTRING(str)->len
   * and pass it to rb_str_* methods */
  return self;
}

> Or, what should I do when I try to open a file in C (the filename
> being passed to the function) and the file doesn't exist?

static VALUE
open_and_use_file(VALUE self, VALUE path_str)
{
  const char *path = StringValueCStr(path_str);
  FILE *stream = fopen(path, "r");
  if (stream == NULL) rb_sys_fail(path); /* does not return */
  /* stream is now ready to use ... */
}

you can use rb_sys_fail() when fread, etc fails as well.

-Charlie