My first guess would be that the XS case ends up loading two different instances of the library and so the XS code is changing the behavior of the "wrong one". Hope that helps. I think that's the best I can do with the information provided.

My first guess would be that the XS case ends up loading two different instances of the library

Yes - I'll try to keep my mind open to that possibility as I plod on. Admittedly, I haven't provided very much for anyone ot work with - though I, myself, don't have much more to work with anyway.

I've written a basic Inline::C script (below my sig) that works fine. It has just 2 functions - namely wrap_eror_handler_off and demo2_e. The first turns off the error handling, and the second enables me to check that the error handling has, in fact, been turned off. (If the error handling is off, demo2_e returns a nan. Otherwise it dies most ungracefully with a 'domain error' from the gsl C library. This is all expected behaviour.)

And I've created a minimalist module (SIS::GSL) that contains the exact same 2 functions (nothing more, nothing less). The XS file that Inline::C generates, and the XS file that I have for SIS::GSL are *identical*, except that whereas Inline::C's XS file specifies:

MODULE = gsl_error_pl_4227    PACKAGE = main
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SIS::GSL's XS file specifies:

MODULE = SIS::GSL    PACKAGE = SIS::GSL
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That's the only difference in the respective XS files. I've even gone so far as to rework SIS::GSL with the XS file containing:

MODULE = SIS::GSL    PACKAGE = main
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That successfully transfers wrap_eror_handler_off and demo2_e into the 'main' namespace, but wrap_eror_handler_off still fails to do what it is supposed to do.

Maybe I need to take a closer look at what the gsl library's gsl_set_error_handler_off is doing.

Thanks, tye.

Cheers,
Rob

use warnings;
use strict;

use Inline C => Config =>
    #BUILD_NOISY => 1,
    #CLEAN_AFTER_BUILD => 0,
    INC => '-IC:/_32/msys/1.0/local/include',
    LIBS => '-LC:/_32/msys/1.0/local/lib -lgslcblas -lgsl';

use Inline C => <<'EOC';

#include <stdio.h>
#include <gsl/gsl_math.h>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_sf_gamma.h>
#include <gsl/gsl_sf_coupling.h>
#include <gsl/gsl_message.h>

void wrap_error_handler_off() {
     gsl_set_error_handler_off();
}

SV * demo2_e(int a1, int a2, int a3, int a4, int a5, int a6, int a7, i
+nt a8, int a9) {
     gsl_sf_result r;
     gsl_sf_coupling_9j_e(a1, a2, a3, a4, a5, a6, a7, a8, a9, &r);
     return newSVnv(r.val);
}


EOC
wrap_error_handler_off();
# '-2' is an invalid argument, so the following
# returns a nan iff error handler is turned off.
# Otherwise it dies with 'domain error'
my $r = demo2_e(4, -2,  4, 3, 3, 2, 1, 1, 2);

print $r, "\n";
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