Re: [Swig-devel] Bug in guile's port example when wrapping for guile 2.0

[William S F. <ws...@fu...>]

On 14/05/13 16:23, Geert Janssens wrote:
> On Tuesday 14 May 2013 08:15:45 William S Fulton wrote:
>
>  > Thanks for doing the class example. Re the port example, I'd be tempted
>
>  > to delete it except it tests some typemaps shipped with SWIG, sigh. I'm
>
>  > not sure what to do, I'll try and debug it myself. Do you know where it
>
>  > abouts it goes wrong? Which line of the Guile code or inside the FILE *
>
>  > typemap?
>
>  >
>
>  > William
>
> When running the ports example in a guile 2 context, you will see this
> output:
>
> 314159
>
> (wrong-type-arg "$name" "Wrong type argument in position ~A: ~S" (1
> #<output: string 90071e0>) (#<output: string 90071e0>))
>
> read_int: error reading from file
>
> read_int: Success
>
> 1075290112
>
> On 1.8 you will get this:
>
> 314159
>
> (wrong-type-arg "$name" "Wrong type argument in position ~A: ~S" (1
> #<output: string 8f3a5d0>) (#<output: string 8f3a5d0>))
>
> 4711
>
> The wrong-type-arg error is expected. It is an illustration in the
> example of what doesn't work.
>
> The difference is in the read_int error.
>
> The runme script first writes a number to stdout (314159). Then it
> writes a number to a file called output.txt (4711). You don't see this
> in the output above, but it happens just before the wrong-type-arg
> illustration is run.
>
> After the wrong-type-arg error, the runme script goes on to read the
> number that was written to output.txt and prints what it found. On 1.8
> it correctly prints 4711 again, on 2.0 it gives an error and then a
> wrong number.
>
> The error is generated when executing line 13 in example.c (fscanf ...).
> The function is called from port_wrap.c, line 1370, which is inside the
> wrapper code for the read_int function.
>
> I did step through the wrapper function in gdb, both in guile 1.8 and
> 2.0 environments, but I couldn't find any difference in behaviour
> between the two. Yet one results in a read error eventually, the other
> doesn't.
>
> That's all I have found so far. I hope you can spot the issue. Otherwise
> it will be something for a guile expert.
>
Thanks for the explanations. After experimenting around I found that 
calling rewind on the file descriptor in C or implementing the 
equivalent guile code using seek, fixed the problem. I've checked in the 
fix with Guile code now.

William