On May 13, 2010, at 8:14 AM, Drew wrote:

> Hello, I'm trying to create an FFI wrapper for an Adobe Framemaker
> automation library.  Here's the sample code in C that I'm trying to re-
> create in Ruby:
> 
> 	IntT j = 0;
> 	UIntT i;
> 	F_IntsT attributes;
> 	F_StringsT strings;
> 
> 	/* Get name of each FontFamily and display it based on whether it is
> visible
> 	 * in PGF Designer. */
> 	strings = F_ApiGetStrings(0, FV_SessionId, FP_FontFamilyNames);
> 	attributes = F_ApiGetInts(0, FV_SessionId, FP_FontFamilyAttributes);
> 	for(i=0; i<attributes.len; i++){
> 		j = attributes.val[i];
> 		if(j & FV_FAMILY_VISIBLE)
> 		F_Printf(NULL,"Family %s\n", strings.val[i]);
> 	}
> 
> 
> F_StringsT looks like this:
> 
> typedef struct {
> 	UIntT len;
> 	StringT *val;
> } F_StringsT;
> 
> StringT is defined as unsigned char *, so I think I'm trying to read
> an array of pointers to strings, or unsigned char **.
> 
> Right now I'm just trying to get the strings in Ruby:
> 
> # in my FFI module FM:
> class FStringsT < FFI::Struct
>    layout :len, :int,
>      :val, :pointer
>  end
> 
> attach_function :FApiGetStrings,[:int,:int,:int], FStringsT.by_value
> 
> # in my script:
> strings = FM.FApiGetStrings(0, FM.FVSessionId, FM.FPFontFamilyNames)
> attributes = FM.FApiGetInts(0, FM.FVSessionId,
> FM.FPFontFamilyAttributes)
> 
> puts strings[:len], attributes[:len] # => 337
> strptr = strings[:val].read_pointer()
> if !( strptr.null? )
>  puts strptr # =>  #<FFI::Pointer:0x3bd0e04>
>  sa = strptr.get_array_of_string(0,strings[:len]).compact # => causes
> seg fault
>  puts sa
> end

Wow, lots of information here.

Let's try to break it down a bit.

Let's eliminate the #compact call. Without it, can you successfully read and access those members?

Do you know that the read to strings[:len], attributes[:len] should output 337? Is that right or a guess?

You have a lot going on here. Please simplify it or the diagnosis may be wrong.

cr