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Moving a variable declaration affects unit test...

Started by King of Men Apr 18, 2015 at 8:34 PM 4 replies 2.3k views

Original Post

Apr 18, 2015 at 8:34 PM

So if I declare my class this way:


private:
  vector<ContractInfo*> obligations;
  map<EconActor*, double> borrowers;
  double discountRate;

then my unit tests fail. But if I do it this way:


private:
  double discountRate;
  vector<ContractInfo*> obligations;
  map<EconActor*, double> borrowers;

they pass. My heart fills with unbounded joy at the thought of tracking this one down...

I suspect I have a destructor somewhere that I ought to have declared virtual, but didn't. Any better guesses?

wintertime

Apr 18, 2015 at 10:12 PM

Maybe you use one member in the constructor for initializing the other and as the construction order depends on their declaration order it may change the outcome.

King of Men

Apr 18, 2015 at 10:31 PM

Nope, the members are all independent. Good one, though - I'll keep it in mind for the future.

King of Men

Apr 18, 2015 at 11:27 PM

Turns out I was looking up an un-initialised variable, interpreting it as double, and consistently getting NaN in one case and some small but numerical value in the other. Not sure why the variable location should so consistently flip me between NaN and number, though. Unless perhaps it is the struct layout that does it; the value in question comes from dereferencing the end of that map.

jpetrie

Apr 18, 2015 at 11:28 PM

You may have changed the size of the class due to additional (or few) pad bytes inserted by the compiler to correctly align the members. Check sizeof(the type) before and after, or use /d1reportSingleClass layout in VS.

alh420

Apr 19, 2015 at 8:39 AM

Turns out I was looking up an un-initialised variable, interpreting it as double, and consistently getting NaN in one case and some small but numerical value in the other. Not sure why the variable location should so consistently flip me between NaN and number, though

Probably just coincidence...

Even though the value in this case is "undefined", in practice, it can be deterministic.

It probably was initialized as part of another object, that then went out of scope, and the memory then reused for this object.

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