RtlInitCodePageTable - NtDoc

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

NTSYSAPI
VOID
NTAPI
RtlInitCodePageTable(
    _In_reads_z_(2) PUSHORT TableBase,
    _Inout_ PCPTABLEINFO CodePageTable
    );

#endif

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This function is documented in Windows Driver Kit.