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Thread: Cannot call function without object

  1. #1
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    Default Cannot call function without object

    Hi. I've got a problem. I have public member function called clear() which looks like this:
    Qt Code:
    1. void MainWindow::clear()
    2. {
    3. tableWidget->clear();
    4. tableWidget_2->clear();
    5. tableWidget_3->clear();
    6. tableWidget_4->clear();
    7. tableWidget_5->clear();
    8. tableWidget_6->clear();
    9. tableWidget_7->clear();
    10. }
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    and when I call it in another member function
    Qt Code:
    1. MainWindow::clear()
    To copy to clipboard, switch view to plain text mode 

    There appear error that I can't call member function MainWindow::clear() without object. What's the problem about? Regards

  2. #2
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    Default Re: Cannot call function without object

    You need something like this:
    Qt Code:
    1. this->clear();
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    or simply call clear().

    The class resolution operator ( :: ) is used when calling static functions.

    But usually, when you're using other member functions, you can just call them. Using "this" is a well known ( some say bad ) Java practice.

    Regards

  3. #3
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    Default Re: Cannot call function without object

    I tried to use only call() but there appear error that clear() is not declared

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    Default Re: Cannot call function without object

    Quote Originally Posted by Salazaar View Post
    I tried to use only call() but there appear error that clear() is not declared
    Where do you want to invoke MainWindow::clear() (i.e. in what method or function)?

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    Default Re: Cannot call function without object

    Quote Originally Posted by marcel View Post
    Using "this" is a well known ( some say bad ) Java practice.
    Not only Java, but Python and PHP too. It's completely unnecessary and makes your code look ugly, but I wonder whether I could have any positive outcomes.

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    Default Re: Cannot call function without object

    If the clear function is within QMainWindow why not put the following in your QMainWindow header file :

    Qt Code:
    1. extern MainWindow *theApp;
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    and then in your .cpp file for MainWindow, someplace at the top :

    Qt Code:
    1. MainWindow *theApp; // I'm presuming MainWindow derives from QMainWindow...
    To copy to clipboard, switch view to plain text mode 

    and in your constructor :

    Qt Code:
    1. theApp = this;
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    This way, you can make calls to the clear function from other classes by :

    Qt Code:
    1. theApp->clear();
    To copy to clipboard, switch view to plain text mode 

    as long as you include the MainWindow header file...

    Regards,
    Steve

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