From: Adam Bozanich <adam.boz@...>
Date: 2008-01-12T11:26:21+09:00
Subject: Re: Copying data into a String inside a C extension

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On Jan 11, 2008 12:40 PM, Tony Arcieri <tony@clickcaster.com> wrote:

> I'm extracting data from a function in C which accepts a pointer to the
> string to dump the data into.
>
> I know the length beforehand, so what I need to do is create a new String
> of
> a given length and pass the pointer to the String's buffer to function
> which
> writes into it.
>
> Currently I'm doing this:
>
>  str = rb_str_buf_new(length);
>  buffer_read(buf, RSTRING_PTR(str), length);
>  RSTRING(str)->as.heap.len = length; /* <-- something tells me this is bad
> */
>  RSTRING_PTR(str)[length] = '\0'; /* sentinel */
>

Hi Tony,

You can pass the null pointer to rb_str_new() like so:

VALUE str = rb_str_new(0,length);

if you follow the call flow, it'll end up in str_new(), which allocates
space for length bytes but only copies the data in if ptr is not null.

-Adam

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