compiler error in calling friend function!!??

[aurora]

i declared a friend function in one class...as shown below...

classa.h

class A
{
public: 
friend void friendFunction(void);
void somefunction(void);
.................
}

class A
{
public: 
friend void friendFunction(void);
void somefunction(void);
.................
}

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classa.cpp

void class A::somefunction() 
{
......
friendFunction();
}

void class A::somefunction() 
{
......
friendFunction();
}

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main.cpp

..........
.............
void frienFunction(void)
{
/* function implementation...*/
}

..........
.............
void frienFunction(void)
{
/* function implementation...*/
}

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but i'm getting compiler error saying that "friendFunction not declared in this class"
please help me whats the wrong here!??

[Santosh Reddy]

You don't need friend functions to do what you are trying to do.

friend (friendship relation) is required when void friendFunction(void) calls A::someFunction(), which you are not doing.

void class A::somefunction() 
{
......
friendFunction();
}

void class A::somefunction() 
{
......
friendFunction();
}

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by the way the class keyword is not required here.

[aurora]

Thank u Santosh...
But my actual problem is i have three different classes....i want a function which can access private variables and functions of all three classes....
Thats why i thought of using friend function... but i'm getting error....is the format in which i declared is correct?

The error u identified "class " in member function implementation is not in actual code, here i made mistake while typing...

[Santosh Reddy]

so show how u are doing it, just copy & paste don't re-type.

[ChrisW67]

From declaration:

friend void friendFunction(void);

friend void friendFunction(void);

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and implementation:

void frienFunction(void)

void frienFunction(void)

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These function names are not the same.

[aurora]

so show how u are doing it, just copy & paste don't re-type.

window.h

#ifndef WINDOW_H
#define WINDOW_H
 
#include <QDialog>
#include <QDir>
 
 
 
 
 
class Window : public QDialog
{
    Q_OBJECT
    friend void friendFunction(void);
 
public:
 
    QString string;
 QString searchKey;
    Window(QWidget *parent = 0);
 
private slots:
    void browse();
    void find();
};

#ifndef WINDOW_H
#define WINDOW_H

#include <QDialog>
#include <QDir>





class Window : public QDialog
{
    Q_OBJECT
    friend void friendFunction(void);

public:

    QString string;
 QString searchKey;
    Window(QWidget *parent = 0);

private slots:
    void browse();
    void find();
};

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window.cpp

#include <QtGui>
 
 #include "window.h"
#include<iostream>
void Window::browse()
 {
     QString directory = QFileDialog::getExistingDirectory(this,
                                tr("Find Files"), QDir::currentPath());
 
   friendFunction();
 
     }
 }

#include <QtGui>

 #include "window.h"
#include<iostream>
void Window::browse()
 {
     QString directory = QFileDialog::getExistingDirectory(this,
                                tr("Find Files"), QDir::currentPath());

   friendFunction();

     }
 }

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main.cpp

#include <iostream>
using namespace std;
 
QString global_var("ABCD");
QString filename;
QString searchKey;
QStringList filenameList;
void friendFunction(void);
 
 
int main(int argc, char *argv[])
{
Q_INIT_RESOURCE(mdi);
 
    QApplication app(argc, argv);
    Window window;
    window.show();
    return app.exec();
 
 
 
 
  }
 
 
 
void friendFunction(void)
{
cout<<"FRIEND CALLED "<<endl;
}

#include <iostream>
using namespace std;

QString global_var("ABCD");
QString filename;
QString searchKey;
QStringList filenameList;
void friendFunction(void);


int main(int argc, char *argv[])
{
Q_INIT_RESOURCE(mdi);

    QApplication app(argc, argv);
    Window window;
    window.show();
    return app.exec();




  }



void friendFunction(void)
{
cout<<"FRIEND CALLED "<<endl;
}

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[Santosh Reddy]

You don't need friend function to do so. Just declare as a regular function

//window.h
#ifndef WINDOW_H
#define WINDOW_H
 
 
#include <QDialog>
#include <QDir>
 
 
extern void friendFunction(void); //<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
 
 
class Window : public QDialog
{
    Q_OBJECT
public:
 
 
    QString string;
    QString searchKey;
    Window(QWidget *parent = 0);
 
 
private slots:
    void browse();
    void find();
};

//window.h
#ifndef WINDOW_H
#define WINDOW_H


#include <QDialog>
#include <QDir>


extern void friendFunction(void); //<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<


class Window : public QDialog
{
    Q_OBJECT
public:


    QString string;
    QString searchKey;
    Window(QWidget *parent = 0);


private slots:
    void browse();
    void find();
};

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//window.cpp
#include <QtGui>
#include "window.h"
#include<iostream>
 
 
void Window::browse()
 {
    QString directory = QFileDialog::getExistingDirectory(this,
                                tr("Find Files"), QDir::currentPath());
    friendFunction();
}

//window.cpp
#include <QtGui>
#include "window.h"
#include<iostream>


void Window::browse()
 {
    QString directory = QFileDialog::getExistingDirectory(this,
                                tr("Find Files"), QDir::currentPath());
    friendFunction();
}

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[ChrisW67]

Assuming that friendFunction() will ultimately need access to private parts of your Window class (it doesn't at the moment as Santosh Reddy points out)...

Line 14 of window.h is a grant of privileges, not a forward declaration of a function friendFunction(), which is what is needed in order for your implementation to compile. Add this line:

void friendFunction();

void friendFunction();

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to the top of window.cpp. This forward declaration would typically be in a header included by the implementations that need to know that the function exists.

[aurora]

You don't need friend function to do so. Just declare as a regular function

//window.h
#ifndef WINDOW_H
#define WINDOW_H
 
 
#include <QDialog>
#include <QDir>
 
 
extern void friendFunction(void); //<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
 
 
class Window : public QDialog
{
    Q_OBJECT
public:
 
 
    QString string;
    QString searchKey;
    Window(QWidget *parent = 0);
 
 
private slots:
    void browse();
    void find();
};

//window.h
#ifndef WINDOW_H
#define WINDOW_H


#include <QDialog>
#include <QDir>


extern void friendFunction(void); //<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<


class Window : public QDialog
{
    Q_OBJECT
public:


    QString string;
    QString searchKey;
    Window(QWidget *parent = 0);


private slots:
    void browse();
    void find();
};

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//window.cpp
#include <QtGui>
#include "window.h"
#include<iostream>
 
 
void Window::browse()
 {
    QString directory = QFileDialog::getExistingDirectory(this,
                                tr("Find Files"), QDir::currentPath());
    friendFunction();
}

//window.cpp
#include <QtGui>
#include "window.h"
#include<iostream>


void Window::browse()
 {
    QString directory = QFileDialog::getExistingDirectory(this,
                                tr("Find Files"), QDir::currentPath());
    friendFunction();
}

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ok thak u santosh...
but what if my function needs to access the private variables of the class?

[nish]

Then it also needs an object of the class to be passed as argument (or if you have some global stuff)

[ChrisW67]

Then it also needs an object of the class to be passed as argument (or if you have some global stuff)

Or it could only access private static members of the class.

[xtofl]

I agree to declare the function as an extern, but not in the class header, rather in the cpp, no?