14.1.4 Input-Output System

The internals of the I/O subsystem have been completely redesigned. The new version should be faster while at the same time providing more functionality and more consistent behavior between operating systems and between stream types.

The semantics of character codes has been fixed as (a superset of) Unicode. Redefining the meaning of character codes is no longer supported.

New features and changes to the SICStus streams (SP_stream) include:

• Streams are binary or text also at the lowest level, e.g. in the C API, and there are separate operations for performing I/O of bytes and characters.
• Streams have a layered design. This makes it possible to add character set translation and other transformations (compression, encryption, automatic character set detection, …) to any stream.
• All streams provide non-blocking operations and are interruptible, e.g. with ^C (‘SIGINT’). This is also true for file streams and under Windows.
• Subject to OS limitations, file names can use Unicode and be of arbitrary length. In particular, under Windows, the Unicode API is used for all operations.
• Limits on file size, file time stamps etc have been removed.
• Error handling has been simplified and made more consistent. In the C API all I/O operations return an error code from a rich set of error codes. Errors during write and close operations are no longer ignored.
• It is possible to wait for I/O ready (both for read and write) on any type of stream. This works for all platforms, including Windows. Select operations wait for the appropriate item type, e.g. until a whole (possibly multi-byte) character can be transferred on a text stream.

Other minor changes:

• Now byte_count/2 can be called only on binary streams.
• at_end_of_stream/[0,1] never blocks. Instead it will fail, i.e. behave as if the stream is not at its end, if the operation would otherwise block. See at_end_of_stream/[0,1] in the SICStus Prolog Manual.