Re: reading a file containing both text and binary data

[mcculley@greatwall.cctt.com (Gene McCulley)]

|> In article <9409022042.aa16676@paris.ics.uci.edu>,
|> self@bordeaux.ICS.UCI.EDU (John Self) writes: 
|> 
|> |> At any point I can tell what the format of the next data item should
|> |> be, but I can't think of an Ada-like way to read different data types
|> |> (including text) from the same file.  I can use rep specs to read any
|> |> single data type by using Sequential_IO, but is there any Ada-like way
|> |> to read a file containing multiple types?  The only ideas I've had so
|> |> far involve instantiating Sequential_IO to read 8 bits at a time and
|> |> pack things into the appropriate data types manually with
|> |> UNCHECKED_CONVERSION.  In some sense I really am doing an "unchecked
|> |> conversion" since the files really are just sequences of bytes that
|> |> were generated by a piece of hardware, but I'd like to have take
|> |> advantage of any nice structuring ideas Ada can give me.
|> 
I am on a project where we are successfully using some Posix bindings to do
just this sort of thing.  The Posix bindings have Generic_Read and Generic_Write
functions that can be instantiated on any type (even unconstrained array types)
and work with a posix file descriptor.  This allows us to open a file, read
500 bytes of one type, then 1000 bytes of another type without playing any
games with Unchecked_Conversion or closing and reopening files.  We had to read
in some very large files generated by a C program.  It was not much fun at all
until we started using the bindings.  These can probably be found at wuarchive.