RegDataTypes Reference

The RegDataTypes enum controls how arguments and return values are passed between Excel and your UDF at the registration level. The choice affects what data your function receives, how much work Excel does before calling you, and what type-text character is emitted in the registration string.

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Enum Values

Public Enum RegDataTypes
    rdtXLOPER12U = 0   ' Raw XLOPER12 (type char: U)
    rdtXLOPER12X = 1   ' Async XLOPER12 (type char: X) — return type only
    rdtXLOPER12Q = 2   ' Coerced XLOPER12 (type char: Q)
    rdtFP12 = 3         ' Numeric array (type char: K%)
    rdtBoolean = 4      ' Boolean (type char: A)
    rdtDouble = 5        ' Double (type char: B)
    rdtLong = 6          ' Long integer (type char: J)
    rdtString1 = 7       ' Null-terminated Unicode (type char: C%)
    rdtString2 = 8       ' Length-counted Unicode (type char: D%)
End Enum

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Detailed Reference

rdtXLOPER12U — Raw XLOPER12 (U)

The default and most flexible type. Excel passes the raw XLOPER12 without modification — your function receives whatever the user provided (number, string, cell reference, array, error, or missing).

Use with BindU() to coerce to the desired type. This is the only type that preserves cell reference information for btSingleCellRef.

Function signature: ByRef pArg As XLOPER12

rdtXLOPER12Q — Coerced XLOPER12 (Q)

Excel resolves cell references to their values before calling your function. A reference to a cell containing 42 arrives as xltypeNum with value 42, not as xltypeSRef. A reference to a range arrives as xltypeMulti.

Use with BindQ(). Slightly less overhead than U for functions that process every element, since it avoids the xlCoerce callback in your code. Cannot extract cell coordinates or sheet names.

Function signature: ByRef pArg As XLOPER12

rdtXLOPER12X — Async XLOPER12 (X)

For asynchronous UDF return types. Excel provides a handle that you use later to deliver the result via xlAsyncReturn. Return type only — not used for arguments.

Note: Not currently tested in tbXLLerator.

rdtFP12 — Numeric Array (K%)

Excel passes a pointer to an FP12 structure: a header with row and column counts followed by a flat array of Double values. All non-numeric cells are converted to 0.0 or cause an error.

Use with ReadFP12() helper. Best for high-performance numeric array processing where you don't need to distinguish errors, blanks, or strings. See FP12 Type.

Function signature: ByVal lpFP12 As LongPtr

rdtDouble — Double (B)

Excel extracts the numeric value directly and passes it as a native Double. No XLOPER12 overhead, no binding step, no heap allocation for the return value.

This is often the fastest option for simple numeric functions, but you lose the ability to return errors, handle non-numeric input gracefully, or detect missing arguments.

Function signature (argument): ByVal arg As Double Function signature (return): As Double

rdtLong — Long Integer (J)

Same as rdtDouble but for 32-bit integers.

Function signature: ByVal arg As Long

rdtBoolean — Boolean (A)

Native boolean pass-through.

Function signature: ByVal arg As Boolean

rdtString1 — Null-Terminated Unicode (C%)

Excel passes a pointer to a null-terminated wide string. Use ReadNullTerminatedString() to convert to a VBA String.

Generally, rdtXLOPER12U with btString is preferred because it handles coercion from numbers and booleans automatically.

Function signature: ByVal lpStr As LongPtr

rdtString2 — Length-Counted Unicode (D%)

Excel passes a pointer to a length-counted wide string (first 2 bytes are the character count). Use ReadCountedString() to convert.

Same recommendation as rdtString1 — prefer rdtXLOPER12U with btString for most cases.

Function signature: ByVal lpStr As LongPtr

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Type-Text Characters

The registration type-text string is built by concatenating one character per argument (plus the return type first). The UDF class does this automatically.

RegDataType	Type char	Notes
rdtXLOPER12U	U	Default for args and return
rdtXLOPER12Q	Q	Pre-coerced XLOPER12
rdtXLOPER12X	X	Async return only
rdtFP12	K%	Two characters
rdtBoolean	A
rdtDouble	B
rdtLong	J
rdtString1	C%	Two characters
rdtString2	D%	Two characters

Behavioral flags are appended after all argument types:

Flag	Type char	Set by
Volatile	!	.Volatile = True
Thread-safe	$	.ThreadSafe = True
Macro-equivalent	#	.MacroEquivalent = True

Example: A thread-safe function returning XLOPER12, taking two Double arguments: type-text = UBB$

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Next Steps

• U vs Q Registration — choosing between U and Q for XLOPER12 arguments
• FP12 Type — using the numeric array type
• Performance Tuning — how registration type affects speed