It is normally not necessary, nor desirable, to set this system property
(or environment variable), but its value will be used, as a fall-back,
at runtime if it cannot be determined automatically during initialization of a
runtime or development system. In this chapter,
SP_PATH is used
as a shorthand, as follows.
SP_PATH is a shorthand for the SICStus Prolog
installation directory, whose default location for SICStus 4.7.0 is
C:\Program Files\SICStus Prolog VC15 4.7.0\.
On UNIX, the default installation directory for SICStus 4.7.0
is /usr/local/sicstus4.7.0/ and
SP_PATH is a shorthand
for the subdirectory lib/sicstus-4.7.0/ of the installation
directory, e.g.: /usr/local/sicstus4.7.0/lib/sicstus-4.7.0/.
See System Properties and Environment Variables for more information.
Type definitions and function declarations for the interface are found in the header file <sicstus/sicstus.h>.
The value of many support functions is a return code, namely:
SP_SUCCESS for success,
SP_FAILURE for failure,
SP_ERROR if an error condition occurred, or if an uncaught
exception was raised during a call from C to Prolog.
If the value is
SP_ERROR, then the macro
SP_errno will return a
value describing the error condition:
SP_error_message() returns a pointer to the diagnostic
message corresponding to a specified error number.
The foreign interface supports wide characters. Whenever a sequence of possibly wide character codes is to be passed to or from a C function it is encoded as a sequence of bytes, using the UTF-8 encoding. Unless noted otherwise the encoded form is terminated by a NUL byte. This sequence of bytes will be called an encoded string, representing the given sequence of character codes. Note that it is a property of the UTF-8 encoding that it does not change ASCII character code sequences.
If a foreign function is specified to return an encoded string, then an
exception will be raised if, on return to Prolog, the actual string is
malformed (is not a valid sequence of UTF-8 encoded characters). The
exception raised is