C++ istream / ostream equivalent ?

[vincent picaud]

Matthias Pleh Wrote:

> 
> >
> > Thank you for your reply and yes that works :)
> >
> > Now i m facing with the following problem, what is the trick for input stream ?
> >
> > ( something like
> >
> > std::istream&  operator>>(std::istream&  in,A&  a)
> > {
> >    //  A.someData<<  in;
> >    return in;
> > }
> >
> > in C++ )
> >
> > I m thinking of the situation when we want to load some data from a file.
> >
> > The toString() trick is okay for saving the object... but how to load it back (something like fromString(char[]) would do the job but it does not exist in Object) ?
> >
> > Anyway thank you, you solved half of my problem :)
> >
> >
> 
> Ther are many posibilities, depending on your further needs! Just have a 
> look at the online dokumentation:
> http://www.digitalmars.com/d/2.0/phobos/phobos.html
> 
> But my first try would be such ..
> (note: I've leaved out error-handling ...)
> 
> module test;
> 
> import std.stdio;
> import std.file;
> 
> class A
> {
>      void writeToFile()  { std.file.write("sample.txt",someData);   }
>      void readFromFile() { someData=cast(string)read("sample.txt"); }
>      void clear()        { someData="n/A\n"; }
>      string toString()   { return someData;  }
> private:
>      string someData="Just some data.
> With anohter line of date.
> Even more data.!";	
> }
> 
> int main(string[] args)
> {
> 	A a=new A;
> 	a.writeToFile();
> 	a.clear();
> 	writeln(a);
> 	a.readFromFile();
> 	writeln(a);
> 	return 0;
> }

thank you for all your answers. I understand the approach, but in the same time, I have the feeling that the C++ way is more convenient. 

Look in C++ , to define I/O  for A,  you do not have to modify your class A and simply have to overload two functions:

std::ostream& operator<<(std::ostream& out,const A& a)
std::istream&  operator>>(std::istream&  in,A&  a)

moreover this smoothly extend the I/O C++ framework without other side effect.

I was expecting to find a similar mecanism in D/Phobos 

Perhaps by overloading some read(), write() functions of the Phobos library, but I do not know if it is "moral" to do that and which phobos functions are concerned... IMHO there is a documentation hole here