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Creating an object without default constructor

This is a discussion on Creating an object without default constructor within the C++ Programming forums, part of the General Programming Boards category; Hi. I have a question about the default constructor. To my best understanding, the compiler will provide me with a ...

  1. #1
    Registered User
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    May 2013
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    219

    Creating an object without default constructor

    Hi.

    I have a question about the default constructor.

    To my best understanding, the compiler will provide me with a deafult constructor only if there are no any user defined constructors, at all.

    now consider the following code:

    Code:
    class MyClass
    {
    private:
        int m_data;
    public:
        MyClass(int init):m_data(init){cout<<"Ctr called"<<endl;}
    };
    
    int main()
    {
        MyClass obj;
    }
    this code won't compile, since there is "no matching function for call to 'MyClass::MyClass()'".
    so far, everything makes sense, since there is no deafult constructor, I can't instantiate a MyClass object without providing one int parameter.

    what confusing me is that this code will compile:

    Code:
    class MyClass
    {
    private:
        int m_data;
    public:
        MyClass(int init):m_data(init){cout<<"Ctr called"<<endl;}
    };
    
    int main()
    {
        MyClass obj(); //added parentheses
    }

    How is it that suddenly, there is a default constructor?
    Last edited by Absurd; 06-24-2013 at 10:03 AM.

  2. #2
    Registered User
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    May 2010
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    3,644
    There's not suddenly a default constructor. What you've done is prototype a function named obj, that returns a MyClass and takes no arguments.

    Jim

  3. #3
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    May 2013
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    219
    Thanks jimblumberg!
    that clears things up.

  4. #4
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    Oct 2006
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    if you define a constructor of any kind, the compiler will not generate the default or copy constructor for you. if you define one, you have to define them all yourself.
    What can this strange device be?
    When I touch it, it gives forth a sound
    It's got wires that vibrate and give music
    What can this thing be that I found?

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