12.4.19 Errors and warnings

PL_warning() prints a standard Prolog warning message to the standard error (user_error) stream. Please note that new code should consider using PL_raise_exception() to raise a Prolog exception. See also section 4.10.

bool PL_warning(format, a1, ...)

Print an error message starting with‘[WARNING: ’, followed by the output from format, followed by a‘]’and a newline. Then start the tracer. format and the arguments are the same as for printf(2). Always returns FALSE.

int PL_fatal_error(format, a1, ...)

As PL_warning(), but using [FATAL ERROR: at <time> ...] and terminates the process after cleanup using abort(). If the process is a Windows GUI application it uses a message box. This function should be used if an unrepairable error is detected. For example, Prolog uses it to signal it cannot find the compiled Prolog startup or memory allocation fails in a place from where we cannot gracefully generate an exception.^{235Currently most memory allocation except for most of the big allocations such as for the Prolog stacks.}

int PL_system_error(format, a1, ...)

As PL_fatal_error(), but using [ERROR: system error:] and provides additional technical details such as the thread that trapped the error and backtrace of the C and Prolog stacks. This function should be used to when an unexpected and unrepairable error is detected. For example, Prolog uses this after it finds an inconsistency in the data during garbage collection.

int PL_api_error(format, a1, ...)

As PL_system_error(), but using [ERROR: API error:] and provides additional technical details such as the thread that trapped the error and backtrace of the C and Prolog stacks. This function is used by the C API and may be used by other language bindings to report invalid use of the API. This function causes the process to be terminated.

bool PL_print_message(atom_t severity, ...)

Calls print_message/2 using a term constructed from the remaining arguments that are passed to PL_unify_term(). This is similar to setting up a call to print_message/2 using PL_call_predicate(), except that it saves and restores possibly pending exceptions and delayed goals. The severity argument must be valid for print_message/2.