Problem with bson_append_double

[Thành Khắc Nguyễn]

Dear All!
When using function bson_append_double, i got this problem.
 
    bson_init(bson_doc);           
    double dvalue = 0.01;
    bson_append_double(pbson, "para.12.errSave", -1,dvalue);

But the result i got when printf is crazy long number  0.0099999999 ...

Did anyone face this problem before, and how to resolve this?
Thanks and Regard.

[Sam Rossi]

Hi Thành! This looks like a general error relating to how most decimal numbers can't be represented exactly in floating point. A quick google leads to a number of great tutorials on the subject, but this one in particular looks like it might be instructive. The basic idea is that only fractions with a denominator of a power of 2 can be expressed exactly in floating point, so all other values are represented as the closest value that can be expressed.

Let me know if you have any other questions!

[Sam Rossi]

I forgot to mention this, but if you need to exactly represent decimal values for some reason, you can also use the BSON decimal type rather than a floating point number.