[PPL-devel] Last problem (hope!)

[Roberto Bagnara]

Enrico Oliosi wrote:
> I used the function set_output_function() how you suggest me.
> When I use it in a single program like in your tests example
> it works correctly, but when I use it in a class I must
> declare it static; I used it in a my_print function in order
> to print the ph for each comand.
> 
> I think that this happens for this reason: since the namespace Variable
> have static member when I used the functions of this namespace in
> a class (an object which can be initialized more times) I must
> declare them static.

Dear Enrico,

what you say above makes little sense to me, and the code you attached
does not clarify the situation.  In general, if you can send us a
complete example (i.e., one that compiles) there are more chances
we can be helpful.  My suggestion is to forget about what you wrote
above and declare `static' what you want to be static and non-static
what you want to be non-static.  Then we will see what the actual
problem is.

> The problem is in this class:
> 
> class Cmd{
> 
> public:
> 
>   //ph which I have in each statement
>   NNC_Polyhedron ph_in;
> 
>   //these are Hashmap the first element is the dimension
>   //and the second the variable to print
>   static map<dimension_type, string> var_to_print;
>   static map<dimension_type, string>::iterator iter;

Why is `iter' a member of the class?

> public:
> 
> static void Cmd::new_output_function(ostream& s, const Variable v) {
>     iter = var_to_print.find(v.id());
>     s << iter->second;
>   }

Why isn't `iter' local to this function?  (And, by the way, why
don't you check whether `v' was actually found or not?)

> void Cmd::print_constraints(const ConSys& cs, const string& intro, 
> ostream& s){
>     using namespace IO_Operators;
> 
>     // Save the default output function.
>     Variable::Output_Function_Type* p_default_output_function =
>       Variable::get_output_function();
> 
>     // Install an alternate output function.
>     Variable::set_output_function(new_output_function);
> 
>     /* Your code of print_constraints() */
> 
>     /* Code to restore the default output function. */
> 
>     [...]
> };

Looks reasonable.

> when I compile it the g++ gives me these errors:
> 
> /tmp/ccOzbfS7.o(.gnu.linkonce.t._ZN3Cmd19new_output_functionERSoN23Parma_Polyhedra_Library8VariableE+0x24): 
> In function `Cmd::new_output_function(std::basic_ostream<char, 
> std::char_traits<char> >&, Parma_Polyhedra_Library::Variable)':
> : undefined reference to `Cmd::var_to_print'
> [...]
> : undefined reference to `Cmd::iter'
> [...]

This seems to be a FAQ, indeed:
see http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.10

I hope this helps.  If not, please come back to us.
All the best,

     Roberto

-- 
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara at cs.unipr.it