Hi folks,
I am trying to implement a friend class and the following is what I did.
Please scroll down.
/*************** ** CODE *************** *************** ****/
class BKP
{
private:
int nVar;
vector<int> p;
vector<int> w;
int b;
public:
BKP();
BKP(ifstream &in);
~BKP();
friend ostream &operator<<( ostream &_os, BKP& _bkp);
};
ostream& operator <<( ostream& _os, BKP& _bkp)
{
for ( int i =0; i <_bkp.nVar ; i++)
{
_os << _bkp.p.at(i) << " " << _bkp.w.at(i) << endl;
}
_os << _bkp.b <<endl;
return _os;
}
I tried to compile in MSVC++ 6.0 and I get the following errors:
error C2248: 'nVar' : cannot access private member declared in class 'BKP'
error C2248: 'p' : cannot access private member declared in class 'BKP'
error C2248: 'w' : cannot access private member declared in class 'BKP'
error C2248: 'b': cannot access private member declared in class 'BKP'
I can't figure this. A friend function is supposed to access the private
members is what I read. Please clarify. thanx for ur time.
srini. 5 2450
Srini nandiraju wrote in news:b6da7d0d.0 405181949.1d79f 9f3
@posting.google .com in comp.lang.c++: I tried to compile in MSVC++ 6.0 and I get the following errors:
MSVC++ 6.0 is your problem, upgrade your compiler. MSVC 7.1 is the
current version if you can live without the IDE its a free download.
Rob.
-- http://www.victim-prime.dsl.pipex.com/
"Srini nandiraju" <na******@ureac h.com> wrote in message
news:b6******** *************** ***@posting.goo gle.com... Hi folks,
I am trying to implement a friend class and the following is what I did. Please scroll down.
/*************** ** CODE *************** *************** ****/ class BKP { private: int nVar; vector<int> p; vector<int> w; int b;
public:
BKP(); BKP(ifstream &in); ~BKP();
friend ostream &operator<<( ostream &_os, BKP& _bkp);
};
ostream& operator <<( ostream& _os, BKP& _bkp) {
for ( int i =0; i <_bkp.nVar ; i++) { _os << _bkp.p.at(i) << " " << _bkp.w.at(i) << endl; } _os << _bkp.b <<endl;
return _os; }
I tried to compile in MSVC++ 6.0 and I get the following errors:
error C2248: 'nVar' : cannot access private member declared in class 'BKP' error C2248: 'p' : cannot access private member declared in class 'BKP' error C2248: 'w' : cannot access private member declared in class 'BKP' error C2248: 'b': cannot access private member declared in class 'BKP'
I can't figure this. A friend function is supposed to access the private members is what I read. Please clarify. thanx for ur time.
That's not what I get when I compile it with VC++ 6.0. I get:
z.cpp(5) : error C2143: syntax error : missing ';' before '<'
z.cpp(5) : error C2501: 'vector' : missing storage-class or type specifiers
z.cpp(5) : error C2059: syntax error : '<'
z.cpp(5) : error C2238: unexpected token(s) preceding ';'
z.cpp(6) : error C2143: syntax error : missing ';' before '<'
And so on and on...
The reason is that you omitted the following:
#include <ostream>
#include <vector>
You also did not include the "std::" qualifier on anything. Without them you
need to use 'using' at least once.
The following compiles without an error, though I don't know why it doesn't
complain about ifstream:
#include <ostream>
#include <vector>
using namespace std;
class BKP
{
private:
int nVar;
vector<int> p;
vector<int> w;
int b;
public:
BKP();
BKP(ifstream &in);
~BKP();
friend ostream &operator<<( ostream &_os, BKP& _bkp);
};
ostream& operator <<( ostream& _os, BKP& _bkp)
{
for ( int i =0; i <_bkp.nVar ; i++)
{
_os << _bkp.p.at(i) << " " << _bkp.w.at(i) << endl;
}
_os << _bkp.b <<endl;
return _os;
}
DW
Srini,
I think what you are seeing is a VC++ 6 bug, I used the .NET
2003 C++ and the code below works ok and prints out what you'd
expect.
dave
+++++++++++++++ +++++++++++++++ +++++++++++++
#include <vector>
#include <iostream>
using namespace std;
class Matrix;
class Vector
{
public:
float v[4];
friend Vector operator*(const Matrix& M, const Vector& V);
};
class Matrix
{
private:
Vector v[4];
public:
friend ostream;
friend ostream& operator<<( ostream& _os, const Matrix& M );
friend Vector operator*(const Matrix& M, const Vector& V);
};
ostream& operator<< ( ostream& _os, const Matrix& M)
{
for ( int i=0; i<4; i++)
for (int j=0; j<4; j++)
{
float x = M.v[i].v[j];
}
return _os;
}
Vector operator*(const Matrix& M, const Vector& V)
{
Vector U;
for (int i=0; i<4; i++)
{
U.v[i]=0;
for (int j=0; j<4; j++)
{
U.v[i] += M.v[i].v[j] * V.v[j];
cout << U.v[i];
}
}
return U;
}
class BKP
{
int nVar;
vector<int> p;
vector<int> w;
int b;
public:
BKP()
{
nVar=10;
b=1;
for (int i=0; i<10; i++)
{
p.push_back(i);
w.push_back(i*i );
}
};
BKP(ifstream &in){};
~BKP(){};
friend ostream& operator<<( ostream& _os, const BKP& _bkp );
};
ostream& operator <<( ostream& _os, const BKP& _bkp)
{
for ( int i =0; i <_bkp.nVar ; i++)
{
_os << _bkp.p.at(i) << " " << _bkp.w.at(i) << endl;
}
_os << _bkp.b <<endl;
return _os;
}
int main()
{
BKP bkp;
cout << bkp;
return 0;
}
"Srini nandiraju" <na******@ureac h.com> wrote in message
news:b6******** *************** ***@posting.goo gle.com... Hi folks,
I am trying to implement a friend class and the following is what I did. Please scroll down.
/*************** ** CODE *************** *************** ****/ class BKP { private: int nVar; vector<int> p; vector<int> w; int b;
public:
BKP(); BKP(ifstream &in); ~BKP();
friend ostream &operator<<( ostream &_os, BKP& _bkp);
};
ostream& operator <<( ostream& _os, BKP& _bkp) {
for ( int i =0; i <_bkp.nVar ; i++) { _os << _bkp.p.at(i) << " " << _bkp.w.at(i) << endl; } _os << _bkp.b <<endl;
return _os; }
I tried to compile in MSVC++ 6.0 and I get the following errors:
error C2248: 'nVar' : cannot access private member declared in class 'BKP' error C2248: 'p' : cannot access private member declared in class 'BKP' error C2248: 'w' : cannot access private member declared in class 'BKP' error C2248: 'b': cannot access private member declared in class 'BKP'
I can't figure this. A friend function is supposed to access the private members is what I read. Please clarify. thanx for ur time.
srini.
"Srini nandiraju" <na******@ureac h.com> wrote in message
news:b6******** *************** ***@posting.goo gle.com... Hi folks,
I am trying to implement a friend class and the following is what I did. Please scroll down.
/*************** ** CODE *************** *************** ****/ class BKP { private: int nVar; vector<int> p; vector<int> w; int b;
public:
BKP(); BKP(ifstream &in); ~BKP();
friend ostream &operator<<( ostream &_os, BKP& _bkp);
};
ostream& operator <<( ostream& _os, BKP& _bkp) {
for ( int i =0; i <_bkp.nVar ; i++) { _os << _bkp.p.at(i) << " " << _bkp.w.at(i) << endl; } _os << _bkp.b <<endl;
return _os; }
I tried to compile in MSVC++ 6.0 and I get the following errors:
error C2248: 'nVar' : cannot access private member declared in class 'BKP' error C2248: 'p' : cannot access private member declared in class 'BKP' error C2248: 'w' : cannot access private member declared in class 'BKP' error C2248: 'b': cannot access private member declared in class 'BKP'
I can't figure this. A friend function is supposed to access the private members is what I read. Please clarify. thanx for ur time.
srini.
This is an MSVC++ 6 bug. Which service pack are you using? I think this was
fixed in the latest service pack.
Another workaround is to move the function into the class
class BKP
{
...
friend ostream &operator<<( ostream &_os, const BKP& _bkp)
{
...
}
};
Also you should declare operator<< with a const reference parameter like I
have done above. operator<< does not change _bkp, so the reference should be
const.
john
In light of John Harrison's post, I'll add that I'm using Service Pack 5 for
my VC++ 6.0.
DW This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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