RdeSB> The following program only compiles (BCB) in a certain
RdeSB> odd condition. If I have the global variable
RdeSB> 'number_of_students_per_class', it DOESN't recognize the
RdeSB> template operator>> defined. If I comment the variable out,
RdeSB> though, it does recognize the operator>>.  But those things
RdeSB> shouldn't have to do with each other, so what's going on?!?
RdeSB>
RdeSB> #include <vector>
RdeSB> [...omitted...]
RdeSB> void main()
RdeSB> {
RdeSB> // whatever
RdeSB> }

Given that you posted this to comp.std.c++, one has to take this as a C++
language standard question.  In which case the answer is that you used `void'
as the return type of `main', your program is thus ill-formed (since it
violates an explicit requirement of the standard), and your C++ compiler,
after emitting a minimum of one diagnostic, is free to do as it likes.  (-:
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The following program only compiles (BCB) in a certain odd condition.
If I have the global variable 'number_of_students_per_class', it DOESN't
recognize the template operator>> defined.
If I comment the variable out, though, it does recognize the operator>>.
But those things shouldn't have to do with each other, so what's going
on?!?

Note: this is specific to vector<>. If I use some simple template class
instead, things work well in either case.
Note also that this only happens to the vector<float> that is a *member*
of
a class, but *not* to the *local* variable. THAT's really puzzling!

Please, any help would be greatly appreciated, since this is a
simplification of a real application whose development is stalled waiting
for this to be solved...

#include <vector>

struct aistream {};

/**************************************************************/
/* Funtion to input vectors in general
/**************************************************************/
template <class T>
aistream& operator>> (aistream& i, std::vector<T>& c)
{
    c;
    // output c somehow
    return i;
}

/**************************************************************/
/* Definition of class 'student'
/**************************************************************/
struct student
{
    std::vector<float> grades;
};

/**************************************************************/
/* Global variable number_of_students_per_class
/**************************************************************/
std::vector<int> number_of_students_per_class;

/**************************************************************/
/* Input grades of student.
/**************************************************************/
aistream& operator>> (aistream& i, student& st)
{
    i >> st.grades; // this DOESN'T match the template operator>> UNLESS
the
global variable is not present.
    return i;
}

/**************************************************************/
/* Input some set of grades
/**************************************************************/
aistream& operator>> (aistream& i, std::vector<float>& grades)
{
    i >> grades; // this DOES match the template operator>> REGARDLESS of
the global variable being present or not.
    return i;
}

void main()
{
// whatever
}



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"Rodrigo de Salvo Braz" <Rodrigo_Braz@brown.edu.nospam> wrote in message
news:8fackc$k3j@cocoa.brown.edu...
> The following program only compiles (BCB) in a certain odd condition.
> If I have the global variable 'number_of_students_per_class', it
DOESN't
> recognize the template operator>> defined.
I heve compiled your program with Microsoft, Borland, gcc, Intel, Sun,
Comeau compilers whether 'number_of_students_per_class' is present or
not.
The only problem is the main function signature. It should be int main().
What are your error messages?

With regards,
Michael Kochetkov.

[skip]



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In article <8fackc$k3j@cocoa.brown.edu>,
  "Rodrigo de Salvo Braz" <Rodrigo_Braz@brown.edu.nospam> wrote:

[...]
> #include <vector>
>
> struct aistream {};
>
> /**************************************************************/
> /* Funtion to input vectors in general
> /**************************************************************/
> template <class T>
> aistream& operator>> (aistream& i, std::vector<T>& c)
> {
>     c;
>     // output c somehow
>     return i;
> }
>
> /**************************************************************/
> /* Definition of class 'student'
> /**************************************************************/
> struct student
> {
>     std::vector<float> grades;
> };
>
> /**************************************************************/
> /* Global variable number_of_students_per_class
> /**************************************************************/
> std::vector<int> number_of_students_per_class;
>
> /**************************************************************/
> /* Input grades of student.
> /**************************************************************/
> aistream& operator>> (aistream& i, student& st)
> {
>     i >> st.grades; // this DOESN'T match the template
>                     // operator>> UNLESS the
>                     // global variable is not present.

 it has nothing to do with the global.
 before you call i >> st.grades
 the overload version, e.g.
 aistream& operator>> (aistream&, std::vector<float>&);
 must be visible.

>     return i;
> }
>
> /**************************************************************/
> /* Input some set of grades
> /**************************************************************/
> aistream& operator>> (aistream& i, std::vector<float>& grades)
> {
>     i >> grades; // this DOES match the template operator>>

 here, you got an infinite recursive call.



Regards

Frank Z.


>                  // REGARDLESS of
> the global variable being present or not.
>     return i;
> }
>
> void main()
> {
> // whatever
> }
>
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