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QPARSE_E_EXPECTING_REGEX
The parser expected a regular-expression operand
QPARSE_E_EXPECTING_REGEX is HRESULT 0x8004166C. Windows documents it as “Expecting regular expression.”
Interpretation
This result belongs to legacy Windows query parsing and is returned while reading the pattern side of a regex construct. The exact condition is: the pattern is empty, lost through escaping or replaced by a delimiter/operator.
Concrete sources
Observability checklist
- Record escaped token before releasing the relevant objects.
- Associate delimiter form with the exact UTC timestamp and correlation identifier.
- Compare failing and known-good values for parser offset under the same provider or handler version.
- Record the source and normalization path of owning property, not only its display form.
Investigation order
- Capture user pattern and escaped token at the call boundary that returns this result.
- Confirm the operation reached reading the pattern side of a regex construct with the intended delimiter form.
- capture user pattern, language-string representation and final query token separately.
Corrective action
Provide a nonempty valid pattern; never substitute .* silently. Retrying identical parser bytes cannot succeed; regenerate the specific token or schema pairing that failed.
What must not be inferred
Neighboring status codes
QPARSE_E_EXPECTING_REGEX_PROPERTY concerns the property target, not the pattern.
Developer and administrator guidance
Reproduction example
Multiple escaping layers remove the only pattern character. Logging final parser input reveals the empty operand.
Official Microsoft references
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