Re: print, writeln etc. fail when calling from C program on Win32

On 04/01/2014 01:42 AM, Kaitain Jones wrote:
> I'm getting caught out at the moment by having any PL clauses that make any
> output-related side-effect calls such as print or writeln fail when calling
> them from my C wrapper on Win32, meaning that the predicate itself fails
> even though I have no interest in the print output in this context (but I
> want to see the output when submitting queries from the SWI repl). I was
> trying to work out if there was a simple way of allowing the print/write
> calls to succeed (in terms of returning true) even if no output was ever
> delivered anywhere. I had a look at the documentation on the SWI knowledge
> base but I found that section a bit sketchy and couldn't glean meaningful
> answers from it.

I think they raise errors, no?  Nothing specifically is arranged, so they
translate whatever write() returns when writing to stdout, etc.

You can do something similar as done in src/pl-ntconsole.c, which rebinds
the I/O streams to use the Windows console functions and achieve Unicode
I/O as well as color output.  You can change the functions doing the I/O
to use the Windows debug output functions or simply discard the output
or whatever you like.

As a final remark, you might have a look at library(debug), which provides
debug/3 for writing debug messages.  It allows selectively enabling or
disabling debug messages, optionally tagging them with the calling thread
and/or a time stamp, redirecting (some) debug channals to a file, etc.
Finally, if your program is compiled in optimized mode, the debug statements
are simply replaced by 'true' and subsequently discarded by the compiler.

	Cheers --- Jan


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