New style headers versus Old style headers

goodredhat's Avatar
Newbie Member
Hi,

Can anyone please tell me why including a new-style header might give completely different results as compared to including the old-style header in the following fairly trivial case ? Using VC++ 6, I write :
Code: CPP
#include <fstream.h>

class CMyLog : public ofstream
{
public :

    CMyLog& operator<<(const char * ptr)
    {
        ofstream::operator<<(ptr);
        return *this;
    }

};

int main()
{
    CMyLog mylog;
    mylog.open("c:\\mylog");
    mylog << "hello world";
    return 0;
}
The mylog file contains the string "hello world". Now just change the first line to use new-style headers, i.e. put in the following

#include <fstream>
using namespace std;

Now the mylog file contains the numeric value of a pointer !

Can anyone please tell me what is going on ? I need urgent help.

Thank you
Manish Jain

Last edited by shabbir; 19Mar2006 at 08:36.. Reason: CPP Syntax highlighting.
0
coderzone's Avatar, Join Date: Jul 2004
Team Leader
Hey it will be interesting to know. I could not get any hint after debugging.
0
shabbir's Avatar, Join Date: Jul 2004
Go4Expert Founder
Hey its simple. Just When you are calling the base class implementation with
ofstream::operator<<(ptr);
Actually you are calling the address of the actual string but the old implementation requires no type casting and so it prints the string but the new one prints the address of the ptr into the file.
0
coderzone's Avatar, Join Date: Jul 2004
Team Leader
Yeah that could be the only reason.
0
goodredhat's Avatar
Newbie Member
ok, so what be the easiest way to get the new-style header to actually the print the string rather than the address ? Merely casting, you might notice, has no effect here.
0
shabbir's Avatar, Join Date: Jul 2004
Go4Expert Founder
Yeah I noticed that. Probably you need to be doing it in a bit different way
Code: CPP
friend ostream & operator << (ostream &out,const char * ptr)
{
    out<<ptr;
    return out;
}