Comments on: 9.3 — Overloading the I/O operators

By: sw1983

sw1983 — Mon, 28 Feb 2011 11:47:58 +0000

Nevermind I’d forgotten to use the namespace. haha, kick myself.

By: sw1983

sw1983 — Mon, 28 Feb 2011 09:48:30 +0000

Hello, my compiler (visual c++ 2010) will not recognise ostream. It is saying it is an undeclared identifier. I’ve double checked and ostream is in the iostream library, I’ve included iostream. I thought it was something I was doing but I have copied and pasted Alex’s code into my program and still I get the same error. What am I missing? I haven’t written the function yet because the syntax gets underlined in red so I know it won’t compile anyway.

#include #include


class Employee

{

private:

	static int  sm_nID;

	int			m_nID ;

	char		m_strName[25];

	double		m_dWage;	
public:

	Employee(char *strName="Blank", double dWage=10.00)

	{

		using namespace std;

		strncpy_s(m_strName, strName, 25);

		m_nID = ++sm_nID;

		m_dWage = dWage;

	}
	char* GetName()

	{

		return m_strName;

	}
	int GetID()

	{

		return m_nID;

	}
	double GetWage()

	{

		return m_dWage;

	}
	void Print()

	{

		using namespace std;

		cout << "Name: " << m_strName << "\t" << "Employee ID: " << m_nID << "\t" <<

			"Wage: " << m_dWage << "\n";

	}
	static void PrintID()

	{

		std::cout << sm_nID;

	}
	friend void ResetName(Employee &cEmployee);

	friend class FriendOfMine;

	/****************************HERE**************************************************/

        friend ostream& operator<< (ostream &out, Employee &cEmployee);

};
/****************************HERE**************************************************/
ostream& operator<< (ostream &out, Employee &cEmployee)

{
}
int Employee::sm_nID = 0;
void ResetName(Employee &cEmployee)

{

	strncpy(cEmployee.m_strName, "Reset", 25);

}
class FriendOfMine

{

public:

	void WageChange(Employee &cEmployee)

	{

		cEmployee.m_dWage = 5;

	}

};
int main()

{

return 0; }

By: C++ output setf:: notes « Petr Stepanov's Blog

C++ output setf:: notes « Petr Stepanov's Blog — Wed, 09 Feb 2011 08:48:33 +0000

[...] insertion operations for all of the built-in data types, and you’ve already seen how you can overload the insertion operator for your own [...]

By: rebelsoul

rebelsoul — Wed, 05 Jan 2011 23:30:04 +0000

Hello Alex,
Thank you for such a good tutorial. I am facing a problem while running the above given code. I am using visual studio 2008, following your code and same input. However in result only the first input variable value is printed the rest are discarded.
Here is a extract after debug.
cPoint {m_dX=6.0000000000000000 m_dY=0.00000000000000000 m_dZ=0.00000000000000000

Could you please guide, why the program is not taking all the value?

By: ARVIND

ARVIND — Wed, 22 Dec 2010 16:27:57 +0000

While overloading output stream operator << as member member function I am getting following error:

ostreamOprt.cpp:32: error: no match for 'operator<<' in 'std::cout << objs'
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:63: note: candidates are: std::basic_ostream& std::basic_ostream
::operator<<(std::basic_ostream&(*)(std::basic_ostream&)) [with _CharT = char, _Traits = std:
:char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:74: note: std::basic_ostream& std::basic_ostream::operator<<(std::basic_ios&(*)(std::basic_ios&)) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:86: note: std::basic_ostream& std::basic_ostream::operator<<(std::ios_base&(*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:121: note: std::basic_ostream& std::basic_ostream::operator<<(long int) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:155: note: std::basic_ostream& std::basic_ostream::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:98: note: std::basic_ostream& std::basic_ostream::operator<<(bool) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:178: note: std::basic_ostream& std::basic_ostream::oper
ator<<(short int) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:189: note: std::basic_ostream& std::basic_ostream::oper
ator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:193: note: std::basic_ostream& std::basic_ostream::oper
ator<<(int) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:204: note: std::basic_ostream& std::basic_ostream::oper
ator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:179: note: std::basic_ostream& std::basic_ostream::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:214: note: std::basic_ostream& std::basic_ostream::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:238: note: std::basic_ostream& std::basic_ostream::operator<<(double) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:219: note: std::basic_ostream& std::basic_ostream::oper
ator<<(float) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:261: note: std::basic_ostream& std::basic_ostream::operator<<(long double) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:284: note: std::basic_ostream& std::basic_ostream::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:307: note: std::basic_ostream& std::basic_ostream::operator<<(std::basic_streambuf*) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:449: note: std::basic_ostream& std::operator<<(std::basic_ostream&, char) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:505: note: std::basic_ostream& std::operator<<(std::basic_ostream
&, char) [with _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:460: note: std::basic_ostream& std::operator<<(std::basic_ostream&, signed char) [with _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:465: note: std::basic_ostream& std::operator<<(std::basic_ostream&, unsigned char) [with _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:567: note: std::basic_ostream& std::operator<<(std::basic_ostre
am&, const char*) [with _CharT = char, _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:612: note: std::basic_ostream& std::operator<<(std::basic_ostream
&, const char*) [with _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:499: note: std::basic_ostream& std::operator<<(std::basic_ostream&, const signed char*) [with _Traits = std::char_traits]
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/ostream:504: note: std::basic_ostream& std::operator<<(std::basic_ostream&, const unsigned char*) [with _Traits = std::char_traits]

Alex can you please explain why?

By: Gammerz

Gammerz — Tue, 10 Aug 2010 13:22:36 +0000

Alex replied to this above:-

Since ostream is a class, ostream& is a reference to an ostream class. Note that we’re also taking an ostream& as a parameter. ostream is typically passed by reference because we don’t want to make a copy of it as we pass it around.

By: Gammerz

Gammerz — Mon, 09 Aug 2010 15:02:54 +0000

When the operator<< function becomes a friend of class Point, it allows us direct access to the member variables m_dX, m_dY and m_dZ. We could avoid making the operator<< a friend of the class Point and instead use member functions GetX(), GetY() and GetZ(), for improved encapsulation. Is this example purely to demonstrate the use of the "friend" command or are we saying this is a preferred method?

By: saini

saini — Mon, 31 May 2010 05:43:15 +0000

would anyone help to understand me why are we passing both the arguments as a reference,and what will happen if we pass them as  value parameters

By: saini

saini — Mon, 31 May 2010 05:39:07 +0000

hi
would anyone help me to understand that why are we passing both the arguments as a reference and what will happen if we pass them as a value parameter

By: awa

awa — Thu, 01 Apr 2010 05:48:31 +0000

#include
using namespace std;

int x = 11;

int& ref()
{
return x;
}

int main()
{
int *ptr = &ref(); //after the return by reference
//takes place, &ref() is &x

*ptr = 12;
cout < < x << endl;

return 0;
}