11.3.2.1 PL_ARITY_AS_SIZE

As of SWI-Prolog 7.3.12, the arity of terms has changed from int to size_t. To deal with this transition, all affecting functions have two versions, where the old name exchanges the arity as int and a new function with name *_sz() exchanges the arity as size_t. If the C macro PL_ARITY_AS_SIZE is defined before loading SWI-Prolog.h, macros are put in place that map the old names to the new functions. Without precautions, the old code is compatible, but the following warning is printed when compiling:

#warning "Term arity has changed from int to size_t."
#warning "Please update your code and use #define PL_ARITY_AS_SIZE 1."

To make the code compile silently again, include SWI-Prolog.h as below and change the types you use to represent arity from int to size_t. Please be aware that size_t is unsigned.

#define PL_ARITY_AS_SIZE
#include <SWI-Prolog.h>