A XmlChan is a specialised form of Channel which supports XML I/O operations. Writing an Object to an XmlChan (using astWrite) will, if the Object is suitable, generate an XML description of that Object, and reading from an XmlChan will create a new Object from its XML description.
Normally, when you use an XmlChan, you should provide "
source"
and "
sink"
functions
which connect it to an external data store by reading and writing the resulting XML
text. By default, however, an XmlChan will read from standard input and write to
standard output.
Alternatively, an XmlChan can be told to read or write from specific text files using the SinkFile and SourceFile attributes, in which case no sink or source function need be supplied.
If "
source"
is NULL and no value has been set for the SourceFile attribute, the
XmlChan will read from standard input instead.
If "
sink"
is NULL, and no value has been set for the SinkFile attribute, the XmlChan
will write to standard output instead.
"
printf"
format specifiers identified by "
%"
symbols in the
normal way. "
options"
string contains "
%"
format specifiers,
then an optional list of additional arguments may follow it in order to supply
values to be substituted for these specifiers. The rules for supplying these are
identical to those for the astSet function (and for the C "
printf"
function). If the external data source or sink uses a character encoding other than ASCII, the supplied source and sink functions should translate between the external character encoding and the internal ASCII encoding used by AST.
A null Object pointer (AST__NULL) will be returned if this function is invoked with the AST error status set, or if it should fail for any reason.