Ofstream filename variable

[cpp]

When I create an instance of ofstream, what is the name of the member
variable that holds the filename?
For example:

ofstream ofs("Output.txt ");
cout << ofs.WhatIsThePa thVariable;

If there isn't a public member variable I can use, then is there at least a
function that displays the filename?

Thanks

[John Harrison]

Re: Ofstream filename variable


"cpp" <cpp@on.the.net > wrote in message
news:Xns949D71B 41BD7Dcpponthen et@24.24.2.165. ..[color=blue]
> When I create an instance of ofstream, what is the name of the member
> variable that holds the filename?[/color]

There is none.
[color=blue]
> For example:
>
> ofstream ofs("Output.txt ");
> cout << ofs.WhatIsThePa thVariable;
>
> If there isn't a public member variable I can use, then is there at least[/color]
a[color=blue]
> function that displays the filename?
>[/color]

No again.

Use a little imagination. Since you opened the file with a file name you
must also be capable of storing that file name somewhere. For instance you
could derive a class from ofstream that stores the filename

class ofstream_with_f ilename : public ofstream
{
public:
void open(const char* fn)
{
ofstream::open( fn);
filename = fn;
}
string get_filename() const { return filename; }
private:
string filename;
};

I hope that gives you the idea, real code would be a little more
sophisticated than the above.

john

[RCS]

Re: Ofstream filename variable

John Harrison wrote:[color=blue]
> class ofstream_with_f ilename : public ofstream
> {
> public:
> void open(const char* fn)
> {
> ofstream::open( fn);
> filename = fn;
> }
> string get_filename() const { return filename; }
> private:
> string filename;
> };
>
> I hope that gives you the idea, real code would be a little more
> sophisticated than the above.
>
> john[/color]

Yes, REAL CODE(tm) would do it like this:

string& get_filename() const { return filename; }

Apart from this, why do you say that "real code" would do it so much
different than your snippet?

Just wondering.

RXX

[Duane Hebert]

Re: Ofstream filename variable


"RCS" <rcs333@online. no> wrote in message news:n4a0c.7274 $rj4.98132@news 2.e.nsc.no...[color=blue]
> Yes, REAL CODE(tm) would do it like this:
>
> string& get_filename() const { return filename; }[/color]

So real code would return a non const reference to
a private member?

How about
const string & get_filename() const { return filename;}

[John Harrison]

Re: Ofstream filename variable


"RCS" <rcs333@online. no> wrote in message
news:n4a0c.7274 $rj4.98132@news 2.e.nsc.no...[color=blue]
> John Harrison wrote:[color=green]
> > class ofstream_with_f ilename : public ofstream
> > {
> > public:
> > void open(const char* fn)
> > {
> > ofstream::open( fn);
> > filename = fn;
> > }
> > string get_filename() const { return filename; }
> > private:
> > string filename;
> > };
> >
> > I hope that gives you the idea, real code would be a little more
> > sophisticated than the above.
> >
> > john[/color]
>
> Yes, REAL CODE(tm) would do it like this:
>
> string& get_filename() const { return filename; }[/color]

No! Three things wrong with that

1) Doesn't compile (non-const reference being taken to const object).
2) Returning reference to internal data member is bad style generally
because it limits your implementation. Suppose you were porting this code to
a O/S where you did have the filename available from some O/S API. How could
you take advantage of that given that you are returning a reference?
3) Most importantly, it's useless functionality. Why would you want to
change the file anme associated with an open file? By return a non-const
reference you are allowing the user to do exactly that.

[color=blue]
>
> Apart from this, why do you say that "real code" would do it so much
> different than your snippet?
>[/color]

I was thinking of two things, implementing all of ofstream constructors in
ofstream_with_f ilename, and error handling, what do you do with the filename
if the open fails (leave it unset presumably). But I was too lazy to
actaully implement that.
[color=blue]
> Just wondering.
>
> RXX
>[/color]

john

[Chris Mantoulidis]

Re: Ofstream filename variable

RCS <rcs333@online. no> wrote in message news:<n4a0c.727 4$rj4.98132@new s2.e.nsc.no>...[color=blue]
> John Harrison wrote:[color=green]
> > class ofstream_with_f ilename : public ofstream
> > {
> > public:
> > void open(const char* fn)
> > {
> > ofstream::open( fn);
> > filename = fn;
> > }
> > string get_filename() const { return filename; }
> > private:
> > string filename;
> > };
> >
> > I hope that gives you the idea, real code would be a little more
> > sophisticated than the above.
> >
> > john[/color][/color]
[color=blue]
> Yes, REAL CODE(tm) would do it like this:
>
> string& get_filename() const { return filename; }
>
> Apart from this, why do you say that "real code" would do it so much
> different than your snippet?
>
> Just wondering.
>
> RXX[/color]

REAL CODE(tm) would do it like this:

const string& get_filename() const { return filename; }

or else the following would have been possible (with your piece of REAL CODE):

ofstream_with_f ilename owf;
owf.open("test. txt");
owf.get_filenam e() = "something" ;

and we don't want the last to happen now do we? ;)