Subj : Re: works only outside class
To   : borland.public.cpp.borlandcpp
From : maeder@glue.ch (Thomas Maeder [TeamB])
Date : Wed Dec 24 2003 02:50 pm

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;
}

.