From: "Aaron D. Gifford" <astounding@...>
Date: 2011-09-10T02:07:45+09:00
Subject: Strings in a Ruby 1.9 C extension?

Hi,

I'm wishing that the Ruby C API had a function like:

VALUE str = rb_str_prealloc(size_t len);

Why?  So I could then do this:

char *c_ptr = RSTRING_PTR(str);
size_t rlen = some_other_c_lib_func(some_input_arg, str, len);

The idea is that I could then call a C function that would use the
preallocated buffer from the Ruby string and fill it fully or
partially.  Then I would need something like:

rb_str_setlen(str, rlen);

The idea is that this function would set the actual string length so
long as rlen is less than or equal to the preallocated size.
Internally, rb_str_setlen(str, rlen) would double-check that rlen
doesn't exceed the allocated buffer size.

QUESTIONs:

Are there any existing C functions like this for Ruby 1.9 (MRI)?  So
far it appears that I'm going to have to roll my own, borrowing code
from the RSTRING_LEN/RSTRING_PTR macros to handle cases where a
preallocation length was very small (<=RSTRING_EMBED_LEN_MAX).

Thanks,
Aaron out.