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Thread: compiler error in calling friend function!!??

  1. #1
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    Default compiler error in calling friend function!!??

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

    classa.h

    Qt Code:
    1. class A
    2. {
    3. public:
    4. friend void friendFunction(void);
    5. void somefunction(void);
    6. .................
    7. }
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    classa.cpp
    Qt Code:
    1. void class A::somefunction()
    2. {
    3. ......
    4. friendFunction();
    5. }
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    main.cpp
    Qt Code:
    1. ..........
    2. .............
    3. void frienFunction(void)
    4. {
    5. /* function implementation...*/
    6. }
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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!??

  2. #2
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    Default Re: compiler error in calling friend function!!??

    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.

    Qt Code:
    1. void class A::somefunction()
    2. {
    3. ......
    4. friendFunction();
    5. }
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    by the way the class keyword is not required here.

  3. #3
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    Default Re: compiler error in calling friend function!!??

    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...

  4. #4
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    Default Re: compiler error in calling friend function!!??

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

  5. The following user says thank you to Santosh Reddy for this useful post:

    aurora (14th November 2011)

  6. #5
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    Default Re: compiler error in calling friend function!!??

    From declaration:
    Qt Code:
    1. friend void friendFunction(void);
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    and implementation:
    Qt Code:
    1. void frienFunction(void)
    To copy to clipboard, switch view to plain text mode 

    These function names are not the same.

  7. The following user says thank you to ChrisW67 for this useful post:

    aurora (14th November 2011)

  8. #6
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    Default Re: compiler error in calling friend function!!??

    Quote Originally Posted by Santosh Reddy View Post
    so show how u are doing it, just copy & paste don't re-type.
    window.h

    Qt Code:
    1. #ifndef WINDOW_H
    2. #define WINDOW_H
    3.  
    4. #include <QDialog>
    5. #include <QDir>
    6.  
    7.  
    8.  
    9.  
    10.  
    11. class Window : public QDialog
    12. {
    13. Q_OBJECT
    14. friend void friendFunction(void);
    15.  
    16. public:
    17.  
    18. QString string;
    19. QString searchKey;
    20. Window(QWidget *parent = 0);
    21.  
    22. private slots:
    23. void browse();
    24. void find();
    25. };
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    window.cpp
    Qt Code:
    1. #include <QtGui>
    2.  
    3. #include "window.h"
    4. #include<iostream>
    5. void Window::browse()
    6. {
    7. QString directory = QFileDialog::getExistingDirectory(this,
    8. tr("Find Files"), QDir::currentPath());
    9.  
    10. friendFunction();
    11.  
    12. }
    13. }
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    main.cpp
    Qt Code:
    1. #include <iostream>
    2. using namespace std;
    3.  
    4. QString global_var("ABCD");
    5. QString filename;
    6. QString searchKey;
    7. QStringList filenameList;
    8. void friendFunction(void);
    9.  
    10.  
    11. int main(int argc, char *argv[])
    12. {
    13. Q_INIT_RESOURCE(mdi);
    14.  
    15. QApplication app(argc, argv);
    16. Window window;
    17. window.show();
    18. return app.exec();
    19.  
    20.  
    21.  
    22.  
    23. }
    24.  
    25.  
    26.  
    27. void friendFunction(void)
    28. {
    29. cout<<"FRIEND CALLED "<<endl;
    30. }
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  9. #7
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    Default Re: compiler error in calling friend function!!??

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

    Qt Code:
    1. //window.h
    2. #ifndef WINDOW_H
    3. #define WINDOW_H
    4.  
    5.  
    6. #include <QDialog>
    7. #include <QDir>
    8.  
    9.  
    10. extern void friendFunction(void); //<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    11.  
    12.  
    13. class Window : public QDialog
    14. {
    15. Q_OBJECT
    16. public:
    17.  
    18.  
    19. QString string;
    20. QString searchKey;
    21. Window(QWidget *parent = 0);
    22.  
    23.  
    24. private slots:
    25. void browse();
    26. void find();
    27. };
    To copy to clipboard, switch view to plain text mode 

    Qt Code:
    1. //window.cpp
    2. #include <QtGui>
    3. #include "window.h"
    4. #include<iostream>
    5.  
    6.  
    7. void Window::browse()
    8. {
    9. QString directory = QFileDialog::getExistingDirectory(this,
    10. tr("Find Files"), QDir::currentPath());
    11. friendFunction();
    12. }
    To copy to clipboard, switch view to plain text mode 

  10. The following user says thank you to Santosh Reddy for this useful post:

    aurora (14th November 2011)

  11. #8
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    Default Re: compiler error in calling friend function!!??

    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:
    Qt Code:
    1. void friendFunction();
    To copy to clipboard, switch view to plain text mode 
    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.

  12. The following user says thank you to ChrisW67 for this useful post:

    aurora (14th November 2011)

  13. #9
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    Default Re: compiler error in calling friend function!!??

    Quote Originally Posted by Santosh Reddy View Post
    You don't need friend function to do so. Just declare as a regular function

    Qt Code:
    1. //window.h
    2. #ifndef WINDOW_H
    3. #define WINDOW_H
    4.  
    5.  
    6. #include <QDialog>
    7. #include <QDir>
    8.  
    9.  
    10. extern void friendFunction(void); //<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    11.  
    12.  
    13. class Window : public QDialog
    14. {
    15. Q_OBJECT
    16. public:
    17.  
    18.  
    19. QString string;
    20. QString searchKey;
    21. Window(QWidget *parent = 0);
    22.  
    23.  
    24. private slots:
    25. void browse();
    26. void find();
    27. };
    To copy to clipboard, switch view to plain text mode 

    Qt Code:
    1. //window.cpp
    2. #include <QtGui>
    3. #include "window.h"
    4. #include<iostream>
    5.  
    6.  
    7. void Window::browse()
    8. {
    9. QString directory = QFileDialog::getExistingDirectory(this,
    10. tr("Find Files"), QDir::currentPath());
    11. friendFunction();
    12. }
    To copy to clipboard, switch view to plain text mode 

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

  14. #10
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    Default Re: compiler error in calling friend function!!??

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

  15. #11
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    Default Re: compiler error in calling friend function!!??

    Quote Originally Posted by nish View Post
    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.

  16. #12
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    Default Re: compiler error in calling friend function!!??

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

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