Finding the name of the object parameter

**circuitbreaker** · 02-11-2008

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.

**CornedBee** · 02-11-2008

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.

**circuitbreaker** · 02-11-2008

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

**Elysia** · 02-11-2008

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.

**cpjust** · 02-11-2008

Originally Posted by Elysia

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>

**Elysia** · 02-11-2008

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.

**anon** · 02-11-2008

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).

**circuitbreaker** · 02-11-2008

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

Thread: Finding the name of the object parameter

Thread Tools

Search Thread

Display

Finding the name of the object parameter

Similar Threads

my error is storage class specified for parameter

Specialising a member function with a template template parameter

Linked List Templates and Object Types

Set Classes