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.WhatIsThePathVariable;

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]

"cpp" <cp*@on.the.net> wrote in message
news:Xn*************************@24.24.2.165...

When I create an instance of ofstream, what is the name of the member
variable that holds the filename?
There is none.
For example:

ofstream ofs("Output.txt");
cout << ofs.WhatIsThePathVariable;

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

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_filename : 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]

John Harrison wrote:

class ofstream_with_filename : 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

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]

"RCS" <rc****@online.no> wrote in message news:n4******************@news2.e.nsc.no...

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

string& get_filename() const { return filename; }

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

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

[John Harrison]

"RCS" <rc****@online.no> wrote in message
news:n4******************@news2.e.nsc.no...

John Harrison wrote:

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

string& get_filename() const { return filename; }

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.


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

I was thinking of two things, implementing all of ofstream constructors in
ofstream_with_filename, 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.
Just wondering.

RXX

john

[Chris Mantoulidis]

RCS <rc****@online.no> wrote in message news:<n4******************@news2.e.nsc.no>...

John Harrison wrote:

class ofstream_with_filename : 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

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

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_filename owf;
owf.open("test.txt");
owf.get_filename() = "something";

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