Using crystal with a C struct of undetermined size

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1

I’m brand new to Crystal. So far I really like what I see. I’ve been experimenting with Crystal’s ability to work with C code. One thing I haven’t been able to figure out so far is what the best way is to work with a C struct with a definition similar to this:

struct string_t {
  unsigned char n;
  char characters[]; 
};

where n is the length of character data in the characters array.

I’m getting a pointer to a struct of string_t from a file, so the format is already defined, and the data is already populated.

I’ve tried this:

@[Extern]
struct ShortString
  @n = uninitialized UInt8
  @characters = uninitialized UInt8[0]
  getter :n
  def characters
    String.new(pointerof(@characters).as(UInt8*), @n)
  end
end

I feel like I’m close, but it doesn’t seem to do what I want. The value for @n seems to be populated correctly. However, the way I’m handling characters must be incorrect, as I’m not seeing the data I’d expect, but I haven’t been able to come up with an alternate formulation that seems to make sense and the compiler is ok with.

Any suggestions for the correct way to handle this?

2

Binding to C flexible array members · Issue #10598 · crystal-lang/crystal · GitHub might help.

3

this is perfect, thank you for the link!