RtlUnicodeStringCchCopyN - NtDoc

#ifndef _NTSTRSAFE_H_INCLUDED_
#ifndef NTSTRSAFE_LIB_IMPL
#ifndef NTSTRSAFE_NO_UNICODE_STRING_FUNCTIONS
#ifndef NTSTRSAFE_NO_CCH_FUNCTIONS

NTSTRSAFEDDI
RtlUnicodeStringCchCopyN(
        _Inout_ PUNICODE_STRING DestinationString,
        _In_ PCUNICODE_STRING SourceString,
        _In_ size_t cchToCopy)
{
    NTSTATUS status;
    wchar_t* pszDest;
    size_t cchDest;

    status = RtlUnicodeStringValidateDestWorker(DestinationString,
            &pszDest,
            &cchDest,
            NULL,
            NTSTRSAFE_UNICODE_STRING_MAX_CCH,
            0);

    if (NT_SUCCESS(status))
    {
        wchar_t* pszSrc;
        size_t cchSrcLength;
        size_t cchNewDestLength = 0;

        status = RtlUnicodeStringValidateSrcWorker(SourceString,
                &pszSrc,
                &cchSrcLength,
                NTSTRSAFE_UNICODE_STRING_MAX_CCH,
                0);

        if (NT_SUCCESS(status))
        {
            if (cchToCopy > NTSTRSAFE_UNICODE_STRING_MAX_CCH)
            {
                status = STATUS_INVALID_PARAMETER;
            }
            else
            {
                if (cchSrcLength < cchToCopy)
                {
                    cchToCopy = cchSrcLength;
                }

                status = RtlWideCharArrayCopyWorker(pszDest,
                        cchDest,
                        &cchNewDestLength,
                        pszSrc,
                        cchToCopy);
            }
        }

        // safe to multiply cchNewDestLength * sizeof(wchar_t) since cchDest < NTSTRSAFE_UNICODE_STRING_MAX_CCH and sizeof(wchar_t) is 2
        DestinationString->Length = (USHORT)(cchNewDestLength * sizeof(wchar_t));
    }

    return status;
}

#endif
#endif
#endif
#endif
View code on GitHub