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Question about functors syntax

This is a discussion on Question about functors syntax within the C++ Programming forums, part of the General Programming Boards category; Hi, All ! I have a doubt regarding some syntax used in functors. For example, we have this: [code] class ...

  1. #1
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    Jun 2013

    Question Question about functors syntax

    Hi, All !
    I have a doubt regarding some syntax used in functors. For example, we have this:

    class myFunctorClass
    myFunctorClass (int x) : _x( x ) {}

    int operator() (int y) { return _x + y; }
    int _x;

    }; [c/ode]

    I know that the essential thing that makes one functor works is overloading the operator(), as shown in the code copied here above.
    But my doubt is regarding the constructor syntax:

     myFunctorClass (int x) : _x( x ) {}
    The only syntax where I have seen that colon ( : ) in a constructor, is the syntax we use in a derived class to inherit from a base class whose constructor needs a parameter.
    So, my question:
    ¿Which is the detailed meaning of this syntax?

     myFunctorClass (int x) : _x( x ) {}
    Thanks in advance!
    Last edited by acerrano; 06-28-2013 at 12:42 PM. Reason: Correcting mistake

  2. #2
    and the hat of int overfl Salem's Avatar
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    It's called an initialisation list.
    10.1 — Constructor initialization lists « Learn C++
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  3. #3
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    If you are using C++11, you can use lambdas instead of functors. They are more convenient.
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    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
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    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

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  4. #4
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    Jun 2013
    Hi !
    Thanks a lot for your answers!
    Elysia: I needed to know about that constructor syntax, even though another function (lambda, for example) may be better to use.

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