Containers and symbolic values

When dealing with symbolic values null and absent, the previous functions are not appropriate. A pair of functions is available to determine whether a container holds a null or absent value; another pair of functions enable you to make a container to hold such a symbolic value.

/* Testing against null or absent */
int xibrt_isNull(xibrt_handle hCtx, xibrt_handle hSource);
int xibrt_isAbsent(xibrt_handle hCtx, xibrt_handle hSource);

/* Making null or absent */
void xibrt_setNull(xibrt_handle hCtx, xibrt_handle hSource);
void xibrt_setAbsent(xibrt_handle hCtx, xibrt_handle hSource);

When retrieving values, always be sure that the container does not hold a symbolic value. A call to xibrt_isNull or xibrt_IsAbsent is almost mandatory before calling any getter function because getter functions s return irrelevant values when the container holds either null or absent.

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