FWIW, I use the following macros to manage sqltype and sqlind:
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#define SQLIND_NOT_NULL 0
#define SQLIND_NULL -1

/* See IB6 API Guide page 92. */
#define XSQLVAR_IS_ALLOWED_TO_BE_NULL(sqlvar) \
((sqlvar->sqltype & 1) != 0)

#define XSQLVAR_IS_NULL(sqlvar) \
(*(sqlvar->sqlind) == SQLIND_NULL)

#define XSQLVAR_SQLTYPE_IGNORING_NULL_FLAG(sqlvar) \
(sqlvar->sqltype & ~1)

#define XSQLVAR_SQLTYPE_READ_NULL_FLAG(sqlvar) \
(sqlvar->sqltype & 1)

#define XSQLVAR_SET_NULL(sqlvar) \
(*(sqlvar->sqlind) = SQLIND_NULL)

#define XSQLVAR_SET_NOT_NULL(sqlvar) \
(*(sqlvar->sqlind) = SQLIND_NOT_NULL)

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These allow me to write C code like:
--------------------------------------------------------
if (
XSQLVAR_IS_ALLOWED_TO_BE_NULL(sqlvar)
&& XSQLVAR_IS_NULL(sqlvar)
) {
// handle a null value
}
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which IMO is more readable than:
--------------------------------------------------------
if (sqlvar->sqltype & 1 == 1 && sqlvar->sqlind == 0) {
// handle a null value
}
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