stream_property/2

stream_property(?stream, ?stream_property) [ISO]

With stream_property/2 it is possible to enumerate all open streams together with all of their properties. This predicate is re-executable as long as there are streams and properties of streams still to enumerate. The standard Prolog properties enumerated are:

end_of_stream/1: is the current stream position at the end or not? The possible values of the argument are: 'at', 'past' or 'not'.
input/0: is the stream an input stream?
output/0: is the stream an output stream?
mode/1: the I/O mode of the stream, thus 'read', 'write' or 'append'.
eof_action/1: what is done when an attempt is made to read past the end of a stream, the possible values of the argument are: 'error', 'eof_code' or 'reset'.
alias/1: one of the possible aliases associated with a stream.
reposition/1: is it possible to reposition the stream? The value of the argument is 'true' or 'false'.
type/1: the type of the stream, the argument is either 'text' or 'binary'.

Trinc-Prolog stream properties

The following stream properties are not part of ISO Prolog standard:

file_name/1: for streams associated with files there is this extra property. The argument of this property is the name of the file that is connected to the stream.
number_format/1: this boolean property indicates if numbers, written to the stream, are formatted according to the number_format_string/1 property or not. For more information see: stream number formatting.
number_format_string/1: this atomic property contains the command string that is used for formatting numbers when they are written to the stream. For more information see: stream number formatting.

Example
open('c:\\temp\\file.txt', write, S), stream_property(S, file_name(N)), close(S), !.	this example opens an output stream, then the filename of the stream is determined by using stream_property/2 and the stream is closed. The cut is to prevent stream_property/2 for finding more solutions.
stream_property(A, S).	the following solutions are generated if the only open streams are the standard input and output streams: A=$stream(2) S=end_of_stream(at) A=$stream(2) S=output A=$stream(2) S=mode(append) A=$stream(2) S=eof_action(reset) A=$stream(2) S=alias(user_output) A=$stream(2) S=reposition(false) A=$stream(2) S=type(text) A=$stream(1) S=end_of_stream(at) A=$stream(1) S=input A=$stream(1) S=mode(read) A=$stream(1) S=eof_action(reset) A=$stream(1) S=alias(user_input) A=$stream(1) S=reposition(false) A=$stream(1) S=type(text) no
stream_property(A, alias(S)).	for each open stream the value of the property alias/1 was unified with S, the solutions generated for the standard streams are: A=$stream(2) S=user_output A=$stream(1) S=user_input no

Exceptions
stream is neither a variable nor a stream term	a domain_error(stream, Stream) exception is thrown, the variable Stream is assigned the incorrect stream term
stream_property is neither a variable nor a valid stream property	a domain_error(stream_property, Stream_property) exception is thrown

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