Re: Reading binary files

["Alex Davies" <alex.mania@...>]

Jeff Wise wrote:
> Again, the data looks like '5A', nnnn, other data
> Where the nnnn is a two byte signed integer (and hi-order byte, low-order
> byte, not Intel format). For example, many length fields are X'2008' 
> meaning
> 8200 bytes. The objective is to count these records. This is complicated 
> by
> the fact that the "other data" may contain '5A' bytes.

Personally I would just write a loop, something similar to: (completely 
untested)

function countrecs(str)
 local count, idx, len = 0, 1, #str
 while idx < len do
   count = count + 1
   assert(str:byte(idx) == 0x5A)
   idx = idx + (str:byte(idx+1)+str:byte(idx+2)*256)
 end
 return count
end

Searching for 0x5As won't help the case, so using byte / substr would be 
quicker then searching the string for them.

Alternatively, make the 0x5A an escape character. This would allow making 
the record header, for example, 5A00, and a true 5A could be 5A5A. This'd be 
more expensive when reading/outputing records, but would allow expansion to 
more special characters.

- Alex