RtlUTF8ToUnicodeN function (wdm.h)
The RtlUTF8ToUnicodeN routine converts a UTF-8 string to a Unicode string.
Syntax
NTSYSAPI NTSTATUS RtlUTF8ToUnicodeN(
[out, optional] PWSTR UnicodeStringDestination,
[in] ULONG UnicodeStringMaxByteCount,
[out] PULONG UnicodeStringActualByteCount,
[in] PCCH UTF8StringSource,
[in] ULONG UTF8StringByteCount
);
Parameters
[out, optional] UnicodeStringDestination
A pointer to a caller-allocated destination buffer into which the routine writes the Unicode output string. If this parameter is NULL, the routine writes the required size of the output buffer to *UnicodeStringActualByteCount.
[in] UnicodeStringMaxByteCount
Specifies the maximum number of bytes that the routine can write to the buffer that UnicodeStringDestination points to. If UnicodeStringDestination = NULL, set UnicodeStringMaxByteCount = 0.
[out] UnicodeStringActualByteCount
A pointer to a location into which the routine writes the actual number of bytes that the routine has written to the buffer that UnicodeStringDestination points to. If UnicodeStringDestination is non-NULL, this count never exceeds the value of UnicodeStringMaxByteCount. If UnicodeStringDestination is NULL, this count is the number of bytes that are required to contain the entire output string.
[in] UTF8StringSource
A pointer to the UTF-8 source string.
[in] UTF8StringByteCount
Specifies the number of bytes in the UTF-8 source string that the UTF8StringSource parameter points to.
Return value
RtlUTF8ToUnicodeN returns STATUS_SUCCESS if the call is successful and all UTF-8 character codes in the input string were converted to the corresponding Unicode character codes in the output string. It returns STATUS_SOME_NOT_MAPPED if the call is successful but one or more input characters were invalid and were converted to the Unicode replacement character, U+FFFD. Possible error return values include the following error codes:
| Return code | Description |
|---|---|
|
The UnicodeStringMaxByteCount parameter specifies a buffer size that is too small to contain the entire output string. |
|
The UnicodeStringDestination and UnicodeStringActualByteCount parameters are both NULL. |
|
The UTF8StringSource parameter is NULL. |
Remarks
The Unicode output string is null-terminated only if the UTF-8 input string is null-terminated.
The routine returns STATUS_BUFFER_TOO_SMALL if the UnicodeStringMaxByteCount parameter specifies a buffer size that is too small to contain the entire output string. In this case, the routine writes as many Unicode characters as will fit in the buffer, and the *UnicodeStringActualByteCount value specifies the number of valid bytes that the routine has written to the buffer. The partial string that is contained in the output buffer might not include a terminating null character.
You can make an initial call to RtlUTF8ToUnicodeN to obtain the required output buffer size, and then call RtlUTF8ToUnicodeN again to obtain the Unicode output string. In the initial call, set UnicodeStringDestination = NULL and UnicodeStringMaxByteCount = 0, and the routine will write the required buffer size to *UnicodeStringActualByteCount. Next, allocate a buffer of the required size and call RtlUTF8ToUnicodeN a second time to obtain the Unicode output string.
RtlUTF8ToUnicodeN supports Unicode surrogate pairs. However, a surrogate leading word value that is not followed by a trailing word value, or a trailing word value that is not preceded by a leading word value, is not recognized as a valid character and is replaced by the Unicode replacement character, U+FFFD.
RtlUTF8ToUnicodeN continues to convert the input string to an output string until it reaches the end of the source buffer or the end of the destination buffer, whichever occurs first. The routine converts any null characters in the input string to null characters in the output string. If the input string contains a terminating null character, but the null character is not located at the end of the source buffer, the routine continues past the terminating null character until it reaches the end of the available buffer space.
The RtlUnicodeToUTF8N routine converts a Unicode string to a UTF-8 string.
You can use the RtlUTF8ToUnicode and RtlUnicodeToUTF8N routines to perform a lossless conversion of valid text strings between the UTF-8 and Unicode formats. However, strings that have arbitrary data values are likely to violate the Unicode rules for encoding surrogate pairs, and any information that is contained in the invalid values in an input string is lost and cannot be recovered from the resulting output string.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Available in Windows 7 and later versions of Windows. |
| Target Platform | Universal |
| Header | wdm.h (include Ntifs.h, Wdm.h, Ntifs.h) |
| Library | NtosKrnl.lib |
| DLL | NtosKrnl.exe |
| IRQL | PASSIVE_LEVEL |