RtlUTF8ToUnicodeN function

Article
01/06/2021

Translates the specified source string into a Unicode string, using the 8-bit Unicode Transformation Format (UTF-8) code page.

Syntax

NTSTATUS WINAPI RtlUTF8ToUnicodeN(
  _Out_     PWSTR  UnicodeStringDestination,
  _In_      ULONG  UnicodeStringMaxByteCount,
  _Out_opt_ PULONG UnicodeStringActualByteCount,
  _In_      PCCH   UTF8StringSource,
  _In_      ULONG  UTF8StringByteCount
);

Parameters

UnicodeStringDestination [out]: A pointer to a caller-allocated buffer that receives the translated string.
UnicodeStringMaxByteCount [in]: Maximum number of bytes to be written at UnicodeStringDestination. If this value causes the translated string to be truncated, RtlUTF8ToUnicodeN returns an error status.
UnicodeStringActualByteCount [out, optional]: A pointer to a caller-allocated variable that receives the length, in bytes, of the translated string. This parameter is optional and can be NULL. If the string is truncated then the returned number counts the actual truncated string count.
UTF8StringSource [in]: A pointer to the string to be translated.
UTF8StringByteCount [in]: Size, in bytes, of the string at UTF8StringSource.

Return value

RtlUTF8ToUnicodeN returns one of the following NTSTATUS values:

Return code	Description
STATUS_SUCCESS	The string was converted to Unicode.
STATUS_SOME_NOT_MAPPED	An invalid input character was encountered and replaced. This status is considered a success status.
STATUS_INVALID_PARAMETER	Both pointers to UnicodeStringDestination and UnicodeStringActualByteCount were NULL.
STATUS_INVALID_PARAMETER_4	The UTF8StringSource was NULL.
STATUS_BUFFER_TOO_SMALL	UnicodeStringDestination was truncated.

Remarks

Although UnicodeStringActualByteCount is optional and can be NULL, callers should provide storage for it, because the received length can be used to determine whether the conversion was successful.

If the output is truncated and an invalid input character is encountered then the function returns STATUS_BUFFER_TOO_SMALL error.

If the UnicodeStringDestination is set to NULL the function will return the required number of bytes to host the translated string without any truncation in UnicodeStringActualByteCount.

RtlUTF8ToUnicodeN does not modify the source string unless the UnicodeStringDestination and UTF8StringSource pointers are equivalent. The returned Unicode string is not null-terminated.

Callers of RtlUTF8ToUnicodeN must be running at IRQL < DISPATCH_LEVEL.

Requirements

Requirement	Value
Minimum supported client	Windows 7 [desktop apps only]
Minimum supported server	Windows Server 2008 R2 [desktop apps only]
Header	Wdm.h
DLL	Ntdll.dll