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# Is it possible to overload the double = (float) operator?

Posted on 2011-02-11
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Is it possible to overload the double = operator?

We're having some trouble with calculations in our software because of the issues converting floats to doubles.  Nearly all variables are floats but there are thousands of calls to DLLs that require doubles and the slight differences are causing problems.

For Example:
``````float fVal = 7.f;
double val = fVal;
``````
The double ends up coming out to something like 7.00000051351

One solution is to convert all our float variables to doubles, but you can imagine how messy that could get.

Maybe I'm barking up the wrong tree and the operator I need to overload is the float () operator to cast it into a double.

I'm not sure if it's even possible.  Just wondering if anyone has any brilliant solution for this.  I haven't found anything after alot of searching.

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Question by:bigsteve87
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Infinity08 earned 2000 total points
ID: 34873095
The assignment operator (or any other operator for that matter) cannot be overloaded for basic types.

If you really want to do this, then you can wrap the float (or double) in a class, and provide an assignment operator for that class. You can then do anything you want in that assignment operator.

However, that wouldn't be the approach I would take. The problem is inherent to floating point types, so either :

(a) consistently use floating point types of the same width (no mixing of float and double)

(b) don't use floating points. Fixed point types can be a better choice. They provide arbitrary precision, and can avoid many of the rounding/precision related problems that floating point types have. The downside is that operations on them are generally slower than floating point types.
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LVL 32

Expert Comment

ID: 34875625
I tried your OP code, and just got 7 (using cout). I've never tried the following before (until now), and not sure if this is OK, so consider it lightly. I added the line
#define float double
and reran the program, and still got 7. I didn't prove anything changed. And since I never did this before, I haven't thought of the ramifications. But if it is legit, then you could add this line to a header file that is included everywhere.
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LVL 53

Expert Comment

ID: 34875728
If you want to change all usage of float to double indiscriminately, it's probably better to do a global find/replace, rather than using a non-intuitive pre-processor macro that is likely to cause a lot of confusion, and will be a maintenance nightmare.
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Author Comment

ID: 34875765
I figured there wasn't an easy way around it.  A global replace is what needs to be done.  Thanks for the help.
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