Is it wrong to compare a double to 0 like this: doubleVariable==0?

问题

It is ok to do this?

double doubleVariable=0.0;
if (doubleVariable==0) {
   ...
}

Or this code would suffer from potential rounding problems?

回答1:

Nope it's perfectly legal if you are only going to compare against 0 as the right side of comparison will automatically casted to double. On the other hand, it would yield all the round-off errors if you where to compare against == 0.10000001

You are better or reading the discussion about float to 0 comparison here: Is it safe to check floating point values for equality to 0?

Also this discussion is very informative about weird precision problems on floats: Why the result is different for this problem?

i.e. below will yield false:

double d1 = 1.000001; double d2 =0.000001;
Console.WriteLine((d1-d2)==1.0);

回答2:

What you have there is 0, which is an integer literal. It is implicitly converted to a double which you could represent with the double literal 0.0 (implicit conversion). Then there is a comparison between the two doubles. A rounding error could cause doubleVariable to not be equal to 0.0 (by some other math you might do, not just setting it), but there could never be a rounding error when converting the integer 0 to double. The code you have there is totally safe, but I would favor == 0.0 instead.

回答3:

Try:

if (double.Equals(doubleValue, 0.0)){}

回答4:

If you're just comparing a double variable against 0.0 (or 0), I believe it's safe to do it that way because I think 0 can be represented exactly in floating point, but I'm not 100% sure.

In general, the suggested approach for comparing floating point numbers is to choose a "delta" value at which you'll consider two doubles to be equal if their difference is less than the delta. This handles exact representation limitations with floating point numbers.

double first = 1.234;
double second = 1.2345;
double difference = Math.Abs(first - second);

double threshold = 0.000001; // doubles are equal if their difference is less than this value - you choose this value based on your needs
bool areEqual = difference < threshold;

回答5:

hmm... I think as long as the number has an exact binary fraction representation (like 0) the comparison is perfectly valid.

回答6:

You should not use double for such comparision. double creates problem.
e.g double n1=0.55 double n2=100 then double ans=n1*n2 should be 55.0
but when you debug ans is 55.000000000000007. if(ans==55.0)
will fail. in such case you can face a problem.

来源：https://stackoverflow.com/questions/5658799/is-it-wrong-to-compare-a-double-to-0-like-this-doublevariable-0

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