RtlUnicodeStringVPrintf - NtDoc

#ifndef _NTSTRSAFE_H_INCLUDED_
#ifndef NTSTRSAFE_LIB_IMPL
#ifndef NTSTRSAFE_NO_UNICODE_STRING_FUNCTIONS

/*++

  NTSTATUS
  RtlUnicodeStringVPrintf(
  _Inout_                      PUNICODE_STRING DestinationString,
  _In_ _Printf_format_string_  PCWSTR          pszFormat,
  _In_                         va_list         argList
  );

  Routine Description:

  This routine is a safer version of the C built-in function 'vsprintf' for
  PUNICODE_STRINGs.

  This function returns an NTSTATUS value, and not a pointer. It returns
  STATUS_SUCCESS if the string was printed without truncation, otherwise it
  will return a failure code. In failure cases it will return a truncated
  version of the ideal result.

Arguments:

DestinationString   -  pointer to the counted unicode destination string

pszFormat           -  format string which must be null terminated

argList             -  va_list from the variable arguments according to the
stdarg.h convention

Notes:
Behavior is undefined if destination, format strings or any arguments
strings overlap.

DestinationString and pszFormat should not be NULL. See RtlUnicodeStringVPrintfEx if you
require the handling of NULL values.

Return Value:

STATUS_SUCCESS -   if there was sufficient space in the dest buffer for
the resultant string

failure        -   the operation did not succeed

STATUS_BUFFER_OVERFLOW
Note: This status has the severity class Warning - IRPs completed with this
status do have their data copied back to user mode
-   this return value is an indication that the print
operation failed due to insufficient space. When this
error occurs, the destination buffer is modified to
contain a truncated version of the ideal result. This is
useful for situations where truncation is ok.

It is strongly recommended to use the NT_SUCCESS() macro to test the
return value of this function

--*/

NTSTRSAFEDDI
RtlUnicodeStringVPrintf(
        _Inout_ PUNICODE_STRING DestinationString,
        _In_ _Printf_format_string_ NTSTRSAFE_PCWSTR pszFormat,
        _In_ va_list argList)
{
    NTSTATUS status;
    wchar_t* pszDest;
    size_t cchDest;

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

    if (NT_SUCCESS(status))
    {
        size_t cchNewDestLength = 0;

        status = RtlWideCharArrayVPrintfWorker(pszDest,
                cchDest,
                &cchNewDestLength,
                pszFormat,
                argList);

        // 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
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