? about this> index::index () : type_intex()

This is a discussion on ? about this> index::index () : type_intex() within the C++ Programming forums, part of the General Programming Boards category; Hello, Can someone tell me what this statement is called, the type_index statement, or how it is used please? () ...

  1. #1
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    ? about this> index::index () : type_intex()

    Hello,

    Can someone tell me what this statement is called, the type_index statement, or how it is used please?

    () : type_index()

    Code:
    in the following context
    
    index::index () : type_index()
    {
        memset(icmomiscp,'\0',sizeof(ICMOMISC));
     
    }
    Thanks very much!
    bk

  2. #2
    ^ Read Backwards^
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    After defining a function like that, you can either initialize your variables in the {} or you can put the colon and initialize whatever you want. This is just calling a function to initialize something. The “: code here” is called the initialization section.

    Code:
    Example::Example() : temp = 0
    {
    //left blank on purpose
    }}
    is the same thing as

    Code:
    Example::Example()
    {
    temp = 0
    }

  3. #3
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    Great! thanks alot that's pretty cool!

    Have a nice weekend!

    bk

  4. #4
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    Syntactically Enahs' example is illegal, it should use a constructor format: temp(0). In your example, type_index might be a member variable, and the empty parenthesis is default-initializing it (to 0 for a built-in or POD type, and with the default constructor for a class type). Also, type_index could be a base class that is being default-initialized.

    Generally using the initializer list is preferred to assigning an initial value inside the constructor block. That is because some members must be initialized in the initializer list, like reference members, and const members. Also, for some class members it is more efficient to use the initializer list, since the class's constructor is called whether you initialize it there or not, and if you assign a new value inside the containing class's constructor body, you are wasting the cpu cycles spent initializing the member class in its default constructor.

  5. #5
    ^ Read Backwards^
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    example is illegal, it should use a constructor format: temp(0).
    He is right.
    I have been arguing with me teacher over:
    example = 5;
    Or
    example(5);

    For a diff situation….I got points deducted off an assignment for using “example(5)” and argue a lot with the teacher about it. But alas, you must do what the teacher said so I have been forcing my self to do the =X way….bad time to relapse sorry!

  6. #6
    ~Team work is the best!~ wakish's Avatar
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    hi..i'm still in learning phase, and i just learned that
    x=6 is the same as x(6)
    infact the x(6) is the constructor method of initialising a class...so initialising a variable like this is legal too!

    well, that's what i just learned, plz if i'm wrong somewhere, do let me know..thanks for ur attention!

    Kind Regards,
    wakish

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