SWI-Prolog -- API-function Snew

Availability:C-language interface function

IOSTREAM* Snew(void *handle, int flags, IOFUNCTIONS *functions)

Create an IOSTREAM* from a handle, flags and a block of callback functions. The flags argument is a bitwise or of SIO_* flags. Flags that control the creation are:

SIO_INPUT
SIO_OUTPUT: One of these flags mut be present to indicate whether this is an input or output stream.
SIO_NBUF
SIO_LBUF
SIO_FBUF: One of these flags must be present to select the buffering as one of unbuffered (SIO_NBUF), line buffered (SIO_LBUF) or fully buffered (SIO_FBUF)
SIO_TEXT: If given, this is a text stream and the encoding is set to the default encoding (see the Prolog flag encoding). Otherwise this is a binary stream and the encoding is set to ENC_OCTET.
SIO_RECORDPOS: If given, enable position maintenance on the stream. This is used by Stell(), Sseek(), stream_property/2 using the position property and related predicates.
SIO_NOMUTEX: Used internally to create a stream that cannot be owned or locked.

If the stream is associated with an OS file handle the system initializes the SIO_ISATTY flag (on POSIX systems) and if possible tells the OS not to inherit this stream to child processes.

The symbol Sfilefunctions is a IOFUNCTIONS struct that contains the callbacks for accessing a regular file. After opening an file using the POSIX open() API we can create a stream to this file using Snew():

  int fno = open(path, O_RDONLY);
  IOSTREAM *s;

  if ( fno >= 0 )
    s = Snew((void*)fno,
             SIO_INPUT|SIO_FBUF|SIO_RECORDPOS|SIO_TEXT,
             &Sfilefunctions);
  ...

Snew() can only fail if there is not enough memory. In that case the return value is NULL and errno is set to ENOMEM.