Subj : Re: works only outside class
To   : borland.public.cpp.borlandcpp
From : Gerhard Wolfstieg <Wolfstieg@t-online.de>
Date : Wed Dec 24 2003 04:43 pm

Thank you for your response in this difficult problem.
I should have mentioned that following line is included (my view was to
close):
typedef unsigned long term_t;
and I add here that the Pl_ function are located in a VC DLL. (it is
SWI-ProLog - I successfully ported the whole into one BC exe file but I
don't have the machine in a BC dll yet)
  The source is near by the minimum -- and a testing frame. I only left out
try and catch and a getchar to have the chance to see something without
setting breakpoints.

     gw

Thomas Maeder [TeamB] wrote:

> Gerhard Wolfstieg <Wolfstieg@t-online.de> writes:
> 
>> Which kind of reasons are conceivable in the following case?
> 
> There is not much difference in the code you show. I'm just giving an
> educated guess here. If I guess wrong, I'm afraid you'll have to reduce
> your program to the absolutely minimal size that still causes the
> behavior you see (<50 lines) and post the result.
> 
> 
>> This code is running fine:
>>>>
>>         int
>> main( int, char *[] )
>> {
>> ...
>>         term_t ref = PL_new_term_ref();
> 
> This initializes ref with the return value of PL_new_term_ref(). In
> principle, the term_t copy constructor is used for this, but it could also
> be be optimized away.
> 
> 
>>         if(  !PL_chars_to_term( "x( A, 2 )", ref )  )
>>                 throw RC_Syntaxfehler;
>> ...
>> }
>> <<
>> The next does not work (it seems to loop in a second thread):
>>>>
>> struct gwTerm
>> {       term_t ref;
>>
>>         gwTerm( char const * );
>> };
>>
>> gwTerm::gwTerm( char const *text )
> 
> Now ref is first default_constructed, since you don't explicitly
> initialize it in the member-initializer list.
> 
> 
>> {       ref = PL_new_term_ref();
> 
> Then you copy-assign the return value of PL_new_term_ref() to ref, using
> term_t's copy-assignment operator.
> 
> 
> If term_t's copy constructor and copy-assignment operator are correctly
> written (or generated), the second version should only be less efficient
> than the first.
> 
> 
> To cause ref to be initialized in the second version like it is
> initialized in the first version, change the constructor implementation to
> 
> gwTerm::gwTerm( char const *text )
>   : ref(PL_new_term_ref())
> {
>   if(  !PL_chars_to_term( text, ref )  )
>     throw RC_Syntaxfehler;
> }

.