Paul Giaccone wrote:
I'm having problems with deserialising floating-point (double) values that are written to an XML file. I'm reading the values back in and comparing them to what I saved to ensure that my file has been written correctly. However, some of the values differ in about the seventeenth significant figure (or thereabouts).
I thought Boost serialization used some numerical limit to make sure that values are serialised exactly to full precision, so what is happening here?
This is a common cause of errors when using floating point values. Writing a floating point value to a string representation, as are XML values, and attempting to read that string representation back, does not guarantee that the floating point value will remain exactly the same since there are a number of floating point values which have no exact representation in the C++ floating point formats. That is simply because of the nature of floating point representation used in C++ and most modern languages. After all, the number of floating point values within any range of numbers is infinite while the C++ floating point representation cab not be. The only way to guarantee what you want for floating point values is to write and read back to a binary representation of the value.