main.c

#include <SWI-Prolog.h>
#include <stdio.h>

int main(int argc, char **argv) {
    // Initialize prolog
    PL_initialise(1, (char*[]){ argv[0]} );

    // Create modules m1 and m2
    module_t m1 = PL_new_module(PL_new_atom("module_1"));
    module_t m2 = PL_new_module(PL_new_atom("module_2"));

    // Fetch and store m2's name inside m2_name_t (re-using the atom created in
    // the line above gives the same result, this is just to show how the error
    // actually happens in my real code)
    atom_t m2_name_a = PL_module_name(m2);
    term_t m2_name_t = PL_new_term_ref();
    PL_put_atom(m2_name_t, m2_name_a);

    // Create a term for "use_module(m2_name_t)"
    term_t use_module_f = PL_new_functor(PL_new_atom("use_module"), 1);
    term_t use_module_t = PL_new_term_ref();
    PL_cons_functor(use_module_t, use_module_f, m2_name_t);

    // Call "use_module(m2_name_t)" inside m1
    PL_call(use_module_t, m1);

    // Fetch exception generated by PL_call
    char *exception_msg;
    term_t exception = PL_exception(0);
    PL_get_chars(exception, &exception_msg, CVT_WRITE | REP_UTF8 | BUF_MALLOC);

    puts(exception_msg); // prints "error(existence_error(source_sink,module_2),_)"
}