Character String Types

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XSD defines many kinds of character string types including string, normalizedString, and token. All of these XSD types are mapped to an OSXMLSTRING type. This internal type represents a UTF-8 character string. The definition of this type in rtxSysTypes.h is as follows:

typedef struct OSXMLSTRING {
 
   OSBOOL cdata;
 
   const OSUTF8CHAR* value;
 
} OSXMLSTRING;
 

The cdata member of this structure is a flag indicating whether or not the value is to be encoded as an XML CDATA section. The value member is a pointer to the string to be encoded. The underlying C type for the OSUTF8CHAR type is unsigned char. This allows the entire UTF-8 character range to be represented as positive numbers.

For C++, the built-in OSXMLSTRING structure is extended to form an XML string class as follows:

class EXTERNRTX OSXMLStringClass : 
 
public OSXMLSTRING, public OSBaseType {
 
 public:
 
   /**
 
    * The default constructor creates an empty string.
 
    */
 
   OSXMLStringClass();
 
   ...
 
} ;
 

 

This makes the data members from the C type available in the C++ case as well. It also adds constructors and other methods to allow the member variables to be initialized and manipulated.

The general mapping is as follows:

XSD type:	<xsd:simpleType name="TypeName"> <restriction base="xsd:string"/> </xsd:simpleType>
Generated C code:	typedef OSXMLSTRING TypeName;
Generated C++ code:	class TypeName : public OSXMLStringClass { ... } ;

In this case, xsd:string refers to the XSD string base type and all other types that are derived from it. A variable of this type can be populated with a simple string literal cast to a const OSUTF8CHAR* variable as follows:

	TypeName strval;
 
	strval.cdata = FALSE;
 
	strval.value = (const OSUTF8CHAR*) "my string";
 

String-based types may be further restricted through the use of facets such as length, minLength, maxLength, and pattern. These have no effect on the generated C type definition. Constraint checks are added to the generated C encoders and decoders to ensure values of the type are within the specified constraint bounds.