RtlUpcaseUnicodeChar - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTRTL_H

/**
 * The RtlUpcaseUnicodeChar routine converts the specified Unicode character to uppercase.
 *
 * \param[in] SourceCharacter Specifies the character to convert.
 * \return The uppercase version of the specified Unicode character.
 * \sa https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/nf-wdm-rtlupcaseunicodechar
 */
NTSYSAPI
WCHAR
NTAPI
RtlUpcaseUnicodeChar(
    _In_ WCHAR SourceCharacter
    );

#endif

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This function is documented in Windows Driver Kit.