Here is my problem:
I have a base class A with operator<< defined to take a template
parameter and append the parameter to a output string stream
(ostringstream). I have a derived class B, which inherits from A and
defines a pure virtual output operator<< taking as a parameter an
enumeration type 'Command' (which is defined in B itself). The point
of the 'Command' enumeration is to have a different implementation of
operator<< when the user sends it an argument of type 'Command'. I
have a final derived class C, which inherits from B and implements
operator<< for parameter type 'Command'. Here is the code describing
my situation (my question to follow after the code):
/* -------- begin code ------------- */
#include <iostream>
#include <sstream>
using namespace std;
class A
{
public:
template<class T>
A &operator<<(const T &Data)
{
OutputBuffer << Data;
}
protected:
ostringstream OutputBuffer;
};
class B:public A
{
public:
enum Command
{
Send
};
using A::operator<<;
virtual bool operator<<(Command) = 0;
};
class C:public B
{
public:
bool operator<<(Command)
{
cout << "You have chosen to send: "
<< OutputBuffer.str() << endl;
}
};
int main(int argc, char *argv[])
{
C c;
B &b = c;
/* (1) */ b << "This is a message" << Send;
}
/* -------- end code ------------- */
My expectation was that (1) would cause operator<< from class A to be
used for the string type and operator<< from class C to be used for
the 'Command' type. However, I find that operator<< from class A is
used for both. Why does this occur?
Thanks
Prashant
3  1529  jo***********@gmail.com wrote:
Here is my problem:
I have a base class A with operator<< defined to take a template
parameter and append the parameter to a output string stream
(ostringstream). I have a derived class B, which inherits from A and
defines a pure virtual output operator<< taking as a parameter an
enumeration type 'Command' (which is defined in B itself). The point
of the 'Command' enumeration is to have a different implementation of
operator<< when the user sends it an argument of type 'Command'. I
have a final derived class C, which inherits from B and implements
operator<< for parameter type 'Command'. Here is the code describing
my situation (my question to follow after the code):
/* -------- begin code ------------- */
#include <iostream>
#include <sstream>
using namespace std;
class A
{
public:
template<class T>
A &operator<<(const T &Data)
{
OutputBuffer << Data;
}
protected:
ostringstream OutputBuffer;
};
class B:public A
{
public:
enum Command
{
Send
};
using A::operator<<;
virtual bool operator<<(Command) = 0;
};
class C:public B
{
public:
bool operator<<(Command)
{
cout << "You have chosen to send: "
<< OutputBuffer.str() << endl;
}
};
int main(int argc, char *argv[])
{
C c;
B &b = c;
/* (1) */ b << "This is a message" << Send;
}
/* -------- end code ------------- */
My expectation was that (1) would cause operator<< from class A to be
used for the string type and operator<< from class C to be used for
the 'Command' type. However, I find that operator<< from class A is
used for both. Why does this occur?
What _type_ does (b << "This is a message") return?
What operator << functions are defined for that type?
V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask jo***********@gmail.com wrote:
Here is my problem:
I have a base class A with operator<< defined to take a template
parameter and append the parameter to a output string stream
(ostringstream). I have a derived class B, which inherits from A and
defines a pure virtual output operator<< taking as a parameter an
enumeration type 'Command' (which is defined in B itself). The point
of the 'Command' enumeration is to have a different implementation of
operator<< when the user sends it an argument of type 'Command'. I
have a final derived class C, which inherits from B and implements
operator<< for parameter type 'Command'. Here is the code describing
my situation (my question to follow after the code):
/* -------- begin code ------------- */
#include <iostream>
#include <sstream>
using namespace std;
class A
{
public:
template<class T>
A &operator<<(const T &Data)
{
OutputBuffer << Data;
}
protected:
ostringstream OutputBuffer;
};
class B:public A
{
public:
enum Command
{
Send
};
using A::operator<<;
virtual bool operator<<(Command) = 0;
};
class C:public B
{
public:
bool operator<<(Command)
{
cout << "You have chosen to send: "
<< OutputBuffer.str() << endl;
}
};
int main(int argc, char *argv[])
{
C c;
B &b = c;
/* (1) */ b << "This is a message" << Send;
}
/* -------- end code ------------- */
My expectation was that (1) would cause operator<< from class A to be
used for the string type and operator<< from class C to be used for
the 'Command' type. However, I find that operator<< from class A is
used for both. Why does this occur?
Thanks
Prashant
The following statement is evaluated left to right.
b << "This is a message" << Send;
First ( b << "This is a message" ) is evaluated. It will return a A&
( reference to A )
Then (ref. to A) << Send; is evaluated. In class A, operator<< is not
virtual, so class A's operator<< is called
On Feb 7, 2:40 am, "Kishore Yada" <yadakish...@gmail.comwrote:
jois.de.vi...@gmail.com wrote:
Here is my problem:
I have a base class A with operator<< defined to take a template
parameter and append the parameter to a output string stream
(ostringstream). I have a derived class B, which inherits from A and
defines a pure virtual output operator<< taking as a parameter an
enumeration type 'Command' (which is defined in B itself). The point
of the 'Command' enumeration is to have a different implementation of
operator<< when the user sends it an argument of type 'Command'. I
have a final derived class C, which inherits from B and implements
operator<< for parameter type 'Command'. Here is the code describing
my situation (my question to follow after the code):
/* -------- begin code ------------- */
#include <iostream>
#include <sstream>
using namespace std;
class A
{
public:
template<class T>
A &operator<<(const T &Data)
{
OutputBuffer << Data;
}
protected:
ostringstream OutputBuffer;
};
class B:public A
{
public:
enum Command
{
Send
};
using A::operator<<;
virtual bool operator<<(Command) = 0;
};
class C:public B
{
public:
bool operator<<(Command)
{
cout << "You have chosen to send: "
<< OutputBuffer.str() << endl;
}
};
int main(int argc, char *argv[])
{
C c;
B &b = c;
/* (1) */ b << "This is a message" << Send;
}
/* -------- end code ------------- */
My expectation was that (1) would cause operator<< from class A to be
used for the string type and operator<< from class C to be used for
the 'Command' type. However, I find that operator<< from class A is
used for both. Why does this occur?
Thanks
Prashant
The following statement is evaluated left to right.
b << "This is a message" << Send;
First ( b << "This is a message" ) is evaluated. It will return a A&
( reference to A )
Then (ref. to A) << Send; is evaluated. In class A, operator<< is not
virtual, so class A's operator<< is called
Excellent! Thank you, that makes perfect sense. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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