External Types

For each external type named <E>, the following two functions are generated, which convert a value of type <E> into its object representation and vice versa:

   sos_Object make_<E>_object (E);
   E          make_<E>        (sos_Object);

For the conversion from sos_Object to <E> a dynamic type check is performed. The object that results from make_<E>_object is of the class sos_Scalar_object; this class is declared in the kernel schema and described in Appendix .

The generated functions will make use of some conversion operations that must be provided by the schema implementor. For this purpose, for each external type named <E>, the file <schema-name>_ext.h must define a C++ type with the same name together with following functions:

void bcopy_from_<E> (void *e, void *c)
void bcopy_to_<E>   (void *e, void *c)

These functions convert a value of type <E> (pointed to by the parameter e) to its standard representation (see also Section ) of n bytes (pointed to by the parameter c) and vice versa.n is the size of the external type as denoted in the external type declaration in the schema. Note that a standard representation of an external type is needed to achieve a language and machine independent storage of objects.

Additionally two functions that convert an external type into an sos_String must be provided, to enable the development of generic I/O routines.

sos_String make_string_from_<E>_object (sos_Object);
sos_Object make_<E>_object_from_string (sos_String);

By convention, the string returned by the first conversion operation has to be created in the TEMP_CONTAINER. It is up to the caller of this function to destroy this string object. Also by convention, the conversion operations should return NO_OBJECT on failure.

Example:

For the type sos_Char, whose standard representation takes one byte, these operations might look as follows:

inline void bcopy_from_sos_Char (void *sos_ch, void *c)
{  *(char*)c = (char*)(sos_Char*)sos_ch; }
inline void bcopy_to_sos_Char (void *sos_ch, void *c)
{  *(sos_Char*)sos_ch = (char*)c; }

sos_String make_string_from_sos_Char_object (sos_Object c)
{  sos_Char s[2];
   s[0] = make_sos_Char (c);  s[1] = '\0';
   sos_String result = sos_String::create (TEMP_CONTAINER);
   result.assign_Cstring (s);
   return result;
}

sos_Object make_sos_Char_object_from_string (sos_String s)
{  sos_Cstring s1 = s.make_Cstring();
   sos_Object  result;
   if (strlen (s1) == 1)  result = make_sos_Char_object (s1[0]);
   else                   result = NO_OBJECT;
   delete s1;
   return result;
}