operator>>

This is a discussion on operator>> within the C++ Programming forums, part of the General Programming Boards category; What does it mean to have operator as a prefix to >>, or != or ==, or any of the ...

  1. #1
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    operator>>

    What does it mean to have operator as a prefix to >>, or != or ==, or any of the other operands?

  2. #2
    and the hat of sweating
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    You mean things like:
    Code:
    bool operator==( const Obj& lhs, const Obj& rhs );
    It's defining a custom operator (i.e. it's a function).

  3. #3
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    Quote Originally Posted by cpjust View Post
    You mean things like:
    Code:
    bool operator==( const Obj& lhs, const Obj& rhs );
    It's defining a custom operator (i.e. it's a function).
    Why do you need custom operators?

  4. #4
    int x = *((int *) NULL); Cactus_Hugger's Avatar
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    So that you can do things like this:
    Code:
    std::cout << "Hello World." << std::endl;
    or this:
    Code:
    std::string str = std::string("Hello") + " World.";
    Generally, when defining operators for classes, try to stay true to the original meaning of the operator. (ie, '+' means 'add')
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  5. #5
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    [QUOTE=Cactus_Hugger;775139]So that you can do things like this:
    Code:
    std::cout << "Hello World." << std::endl;
    or this:
    Code:
    std::string str = std::string("Hello") + " World.";
    So its like, you could assign them in a different way, or use operators in a different way for classes???

  6. #6
    In the Land of Diddly-Doo g4j31a5's Avatar
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    Just like Cactus_Hugger said, you usually need to overload certain operators of an object (e.g. the copy constructor / '=', or comparisons like <, ==, or >). So, if it's not overloaded, it won't do what you want it to do.

    E.g. a class 'Matrix' to define a 3d matrix. If you haven't overloaded the 'equal to' operator and call this:
    Code:
    class Matrix
    {
       private:
          float x;
          float y;
          float z;
    ...
    }
    Matrix a, b;
    ....
    if (a == b)
    {
    ...
    }
    It would mostly returned a false because it wouldn't compare the values of the x, y, z. Now, if you do an operator overload like:
    Code:
    class Matrix
    {
       private:
          float x;
          float y;
          float z;
       public:
          bool operator=(const Matrix &operand)
          {
                return ((this->x == operand->x) &&
                            (this->y == operand->y) &&
                            (this->z == operand->z) &&);
          }
    }
    It would compare between two matrices just like you wanted it to.
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  7. #7
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    Quote Originally Posted by g4j31a5 View Post
    Just like Cactus_Hugger said, you usually need to overload certain operators of an object (e.g. the copy constructor / '=', or comparisons like <, ==, or >). So, if it's not overloaded, it won't do what you want it to do.

    E.g. a class 'Matrix' to define a 3d matrix. If you haven't overloaded the 'equal to' operator and call this:
    Code:
    class Matrix
    {
       private:
          float x;
          float y;
          float z;
    ...
    }
    Matrix a, b;
    ....
    if (a == b)
    {
    ...
    }
    It would mostly returned a false because it wouldn't compare the values of the x, y, z. Now, if you do an operator overload like:
    Code:
    class Matrix
    {
       private:
          float x;
          float y;
          float z;
       public:
          bool operator=(const Matrix &operand)
          {
                return ((this->x == operand->x) &&
                            (this->y == operand->y) &&
                            (this->z == operand->z) &&);
          }
    }
    It would compare between two matrices just like you wanted it to.
    Cool.. But wouldn't you need bool operator==(const Matrix &operand) instead?

  8. #8
    In the Land of Diddly-Doo g4j31a5's Avatar
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    Quote Originally Posted by bobbelPoP View Post
    Cool.. But wouldn't you need bool operator==(const Matrix &operand) instead?
    Oh right. Sorry, it's 1 hour to go before the end of the workday (yay!). So my head is kinda messed up right now.
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  9. #9
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    Quote Originally Posted by g4j31a5 View Post
    Oh right. Sorry, it's 1 hour to go before the end of the workday (yay!). So my head is kinda messed up right now.
    Ah, well thanks anyway, but can it be anything besides &operand? I dont know what &operand is?

  10. #10
    C++まいる!Cをこわせ! Elysia's Avatar
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    The type is const Matrix& (this is why I prefer to type const Matrix& something and not const Matrix &something).
    Essentially, it takes a (const) reference (the &) to an object of type Matrix.
    Const reference means it cannot modify the object.

    But it can be anything you like. So long as it makes sense.
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