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uxsdcxx is a tool to generate PugiXML-based C++ reader, validator and writer from an XSD schema. It can generate code for a subset of XSD 1.0.

It currently supports:

• Simple types with following exceptions:
  • xs:lists are just read into a string.
  • Only enumerations are supported asxs:restrictions of simple types.
  • Restricted string types such asIDREF,NCName etc. aren't validated.
• Complex types.
• Model groups(all, sequence and choice)
• Elements.
• Attributes exceptxs:anyAttribute.
  • Default values are supported.
  • When writing, non-zero default values are always written out.

It currently does not support:

• Anything that PugiXML can't read:
  • XML namespaces

pip install uxsdcxx. Use withuxsdcxx.py foo.xsd. Two filesfoo_uxsdcxx.h andfoo_uxsdcxx.cpp will be created.

All uxsdcxx functions live in anamespace uxsd.

For every root element in the schema, a class is generated withload andwrite functions. For instance,

<xs:elementname="foo">  <xs:complexType>  ...  </xs:complexType></xs:element>

results in this C++ code:

classfoo :publict_foo {public:    pugi::xml_parse_resultload(std::istream &is);voidwrite(std::ostream &os);};

load() loads from an input stream into this root element's structs andwrite() writes its content to a given output stream.

Note that root elements with simple types are not supported.

uxsdcxx generates global pools to store multiply-occurring types.

<xs:complexTypename="foo">  <xs:sequence>    <xs:elementname="bar"type="bar"maxOccurs="unbounded"/>  </xs:sequence></xs:complexType>

generates:

extern std::vector<t_bar> bar_pool;[...]structfoo {    collapsed_vec<t_bar, bar_pool> bars;};

Acollapsed_vec is a size and an offset pointing into a pool. It provides contiguous memory while being able to store an unbounded number of elements. The main limitation of acollapsed_vec is that it's insertable only when its end points to the end of the pool.

Strings constitute a special case: achar_pool is generated for them to prevent many small allocations.

<xs:complexTypename="foo">  <xs:sequence>    <xs:elementname="bar"type="string"maxOccurs="unbounded"/>  </xs:sequence></xs:complexType>

generates:

extern char_pool_impl char_pool;structfoo {constchar * bar;};

The pools are freed by using utility functionsuxsd::clear_pools() anduxsd::clear_strings().clear_strings is provided separately since it can be useful to keep the strings around after freeing the generated structures.

You can find the generated types for your schema in output header filefoo_uxsdcxx.h. The mapping rules of XSD types to C++ types are such:

• <xs:complexType> definitions correspond to C++ structst_{name}. For complexTypes in global scope,name refers to thename attribute of the type. For complexTypes defined inside elements,name refers to thename attribute of the parent element.

  • An<xs:attribute> generates a struct field with a C++ type corresponding to its<xs:simpleType> as defined below.
  • A model group such as<xs:choice>,<xs:sequence> or<xs:all> generates struct fields with C++ types corresponding to the types of the elements inside.
    • If an element can occur more than once, acollapsed_vec<T, T_pool> is generated.
    • If an element can occur zero times, another fieldbool has_T is generated to indicate whether the element is found.

• <xs:simpleType> can take many forms.

• <xs:union> corresponds to a tagged union type, such as:

structunion_foo {    type_tag tag;union {double as_double;int as_int;    };};

• <xs:list> generates aconst char *.
• Atomic builtins, such asxs:string orxs:int generate a field of the corresponding C++ type(const char *,int...)
• <xs:restriction>s of simple types are not supported, except one case where an<xs:string> is restricted to<xs:enumeration> values. C++ enums are generated for such constructs. As an example, the following XSD:

<xs:simpleTypename="filler">  <xs:restrictionbase="xs:string">    <xs:enumerationvalue="FOO"/>    <xs:enumerationvalue="BAR"/>    <xs:enumerationvalue="BAZ"/>  </xs:restriction></xs:simpleType>

generates a C++ enum:

enum class enum_filler {UXSD_INVALID = 0, FOO, BAR, BAZ};