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Calling a constructor on a non-pointer after its declaration.

This is a discussion on Calling a constructor on a non-pointer after its declaration. within the C++ Programming forums, part of the General Programming Boards category; Hello. let's say I have the following class: Code: class A { public: A(int x) :x(x) {} private: int x; ...

  1. #1
    Registered User
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    May 2006
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    Calling a constructor on a non-pointer after its declaration.

    Hello. let's say I have the following class:

    Code:
    class A
    {
    public:
         A(int x) :x(x) {}
    
    private:
         int x;
    };
    Now let's say I also have the following class:

    Code:
    class B
    {
         public:
         B();
    
         private:
         A a;
    };
    
    B::B()
    {
        a.A(5); // invalid
    }
    How do I fix that call to A's constructor without changing a to a pointer or something?

  2. #2
    Registered User
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    The same way as you initialize x in class A.

    Code:
    B::B() : a(5)
    laserlight likes this.

  3. #3
    Registered User
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    May 2006
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    In the program I'm making right now though, I'm having to initialize a in something other than B's constructor though. kind of like this:

    Code:
    class B
    {
    public:
         void run();
    
    private:
         A a;
    };
    
    void B::run()
    {
         a.A(5); // invalid
    }

  4. #4
    C++ Witch laserlight's Avatar
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    By the time the B object is constructed, its A member variable has been constructed, so it is too late to initialise it. You must either provide A with a default constructor, or initialise A with some default int value, and then later change it.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  5. #5
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    Thanks!

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