[Main]
Name=HS_NULL
Type=Constant
Header Files=vat.h
Definition=#define HS_NULL ((HSym) {0, 0})

[Description]
A null symbol constant.

[Explanation]
HS_NULL is a null symbol. Many TIOS functions returns such a symbol
in case of an error. Note that you can't check whether a some variable is HS_NULL using
the "==" operator because HS_NULL is not scalar, i.e. you can't
write something like
<PRE>if (hs == HS_NULL) ...
</PRE>
Instead, check the <I>folder</I> field of <A HREF="$$LINK(HSym)">HSym</A> structure: if it is zero,
the whole structure is HS_NULL, because TIOS never creates <A HREF="$$LINK(HSym)">HSym</A>
structures in which the <I>folder</I> field is zero and the <I>offset</I> field is nonzero.
