eturn strings are called outside the context of a foreign predicate or a foreign predicate creates many strings during its execution. Temporary strings are scoped using these macros:

void PL_STRINGS_MARK()

void PL_STRINGS_RELEASE()

These macros must be paired and create a C block ({...}). Any string created using BUF_STACK after PL_STRINGS_MARK() is released by the corresponding PL_STRINGS_RELEASE(). These macros should be used like below

  ...
  PL_STRINGS_MARK();
  <operations involving strings>
  PL_STRINGS_RELEASE();
  ...