[xsd-users] double values precision

[Boris Kolpackov]

Hi Daniel,

Daniel Oliva <doliva at magaya.com> writes:

> I would like to format double values so during serialization they
> contain only two decimals.

Quoting from examples/cxx/tree/custom/double/README:

This example shows how to customize parsing and serialization code for the
xsd:double XML Schema built-in type using the type customization mechanism
provided by the C++/Tree Mapping. For more information on type customization
see the C++/Tree Mapping Customization Guide, particularly sections 1 and 4:

http://wiki.codesynthesis.com/Tree/Customization_guide

In this example our schema uses xsd:double to represent a price. There are
two potential problems with this choice of a price type. First, xsd:double
can be serialized in the scientific notation which would be an unusual way
of representing a price. Second, we would like to limit the number of 
fraction digits in our prices to 2. Furthermore, we would like to always
have two fraction digits, even if one or both of them are zeros, for
example: 12.99, 12.90, 12.00.

In case we can modify the schema, a better approach would be to define the
price type as a restriction of the xsd:decimal type (always fixed notation)
and specify the fractionDigits facet to limit the number of fraction digits
to 2. However, there is no way in XML Schema to specify that there should
always be exactly 2 fraction digits. Therefore, it may still be desirable
to customize this price type to get the required serialization behavior.

Finally, it is worth noting that the behavior achieved in this example via
type customization can also be achieved by compiling your code with the
following macros defined:

XSD_TREE_DOUBLE_FIXED
XSD_TREE_DOUBLE_PRECISION 2

However, the type customization approach while requiring more work is
cleaner since it does not rely on global macro definitions.

Boris