Finding the name of the object parameter

This is a discussion on Finding the name of the object parameter within the C++ Programming forums, part of the General Programming Boards category; I am writing a class for matrices by the name of Matrix. I have an empty constructor Matrix() where I ...

  1. #1
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    Finding the name of the object parameter

    I am writing a class for matrices by the name of Matrix. I have an empty constructor Matrix() where I initialize the dimensions (rows and columns) of the matrix to zero. This is because I would like the user in the main program to set the dimensions through another overloaded constructor or other explicit means. However, in case the user fails to set the dimensions of the object of class Matrix, the dimensions will remain at 0. I have written the following function that checks for undefined dimensions that works:

    Code:
    	void dimension_check(const Matrix &mat2) const {
    		if ((mat2.rows==0)&&(mat2.columns==0)) {
    			cout << "Error. Matrix dimensions undefined.\n";
    			exit(1);
    		}
    		return;
    	}
    I would like to make a change where it will print an error output giving the name of the object that has not been defined.

    i.e in the main program if I define

    Code:
    Matrix ABC;
    The error message should read "Error. Matrix ABC dimensions undefined." Thus the user will know where the error is.

    Thanks.

  2. #2
    Cat without Hat CornedBee's Avatar
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    That's impossible. C++ does not retain the names of local variables (or anything really, from the viewpoint of the program code) at runtime.

    The only thing you can do is pass the name explicitly. But that's considerably more effort than it's worth.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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    Thanks CornedBee. I'll give up on this one.

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    A better idea is to place an ASSERT instead.
    You don't want the user to see that, do you? With an ASSERT, then program will break when the condition is met and you can take a look at the stack to see in what object the problem occurred.
    Quote Originally Posted by Adak View Post
    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.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  5. #5
    and the hat of sweating
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    Quote Originally Posted by Elysia View Post
    A better idea is to place an ASSERT instead.
    You don't want the user to see that, do you? With an ASSERT, then program will break when the condition is met and you can take a look at the stack to see in what object the problem occurred.
    I think ASSERT() is Windows specific.
    The standard assert() is defined in <cassert>

  6. #6
    C++まいる!Cをこわせ! Elysia's Avatar
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    ASSERT (uppercase) is MFC I believe. But the name of it is the same, it's just how you write it that's different.
    So yes, assert from cassert is what you should use.
    Quote Originally Posted by Adak View Post
    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.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  7. #7
    The larch
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    It is entirely possible to do this with a macro (just like assert works):

    Code:
    #include <iostream>
    
    #define ASSERT_DIMENSION(x) \
        do \
        { \
            if (!x.assert_dimension()) \
            { \
                std::cout << "Dimension is not set for " << #x << '\n'; \
            } \
        } while(0)
    
    class Matrix1
    {
        public:
            Matrix1(int n = 0): d(n) {}
            bool assert_dimension() const { return d != 0; }
        private:
            int d;
    };
    
    int main()
    {
        Matrix1 a(32), b;
        ASSERT_DIMENSION(a);
        ASSERT_DIMENSION(b);
    }
    Of course, there's no need to roll your own (probably broken) assert when there's a perfectly good assert (and there's no need for a function dimension_check as the condition to assert is very simple).
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  8. #8
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    Thanks anon, Elysia and cpjust. I'll read up more on this assert().

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