RtlUnicodeToMultiByteN - NtDoc

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

/**
 * The RtlUnicodeToMultiByteN routine translates the specified Unicode string into a new character string, using the current system ANSI code page (ACP).
 * The source string is not necessarily from a multibyte character set.
 *
 * \param MultiByteString Pointer to a caller-allocated buffer to receive the translated string. MultiByteString buffer must not overlap with UnicodeString buffer.
 * \param MaxBytesInMultiByteString Maximum number of bytes to be written to MultiByteString. If this value causes the translated string to be truncated, RtlUnicodeToMultiByteN does not return an error status.
 * \param BytesInMultiByteString Pointer to a caller-allocated variable that receives the length, in bytes, of the translated string. This parameter is optional and can be NULL.
 * \param UnicodeString Pointer to the Unicode source string to be translated.
 * \param BytesInUnicodeString Size, in bytes, of the string at UnicodeString.
 * \return NTSTATUS Successful or errant status.
 * \sa https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ntifs/nf-ntifs-rtlunicodetomultibyten
 */
NTSYSAPI
NTSTATUS
NTAPI
RtlUnicodeToMultiByteN(
    _Out_writes_bytes_to_(MaxBytesInMultiByteString, *BytesInMultiByteString) PCHAR MultiByteString,
    _In_ ULONG MaxBytesInMultiByteString,
    _Out_opt_ PULONG BytesInMultiByteString,
    _In_reads_bytes_(BytesInUnicodeString) PCWCH UnicodeString,
    _In_ ULONG BytesInUnicodeString
    );

#endif

View code on GitHub
// ntifs.h

NTSYSAPI NTSTATUS RtlUnicodeToMultiByteN(
  [out]           PCHAR  MultiByteString,
  [in]            ULONG  MaxBytesInMultiByteString,
  [out, optional] PULONG BytesInMultiByteString,
  [in]            PCWCH  UnicodeString,
  [in]            ULONG  BytesInUnicodeString
);
View the official Windows Driver Kit DDI reference

NtDoc

This function is documented in Windows Driver Kit.

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Windows Driver Kit DDI reference (nf-ntifs-rtlunicodetomultibyten)

RtlUnicodeToMultiByteN function

Description

The RtlUnicodeToMultiByteN routine translates the specified Unicode string into a new character string, using the current system ANSI code page (ACP). The translated string is not necessarily from a multibyte character set.

Parameters

MultiByteString [out]

Pointer to a caller-allocated buffer to receive the translated string. MultiByteString buffer must not overlap with UnicodeString buffer.

MaxBytesInMultiByteString [in]

Maximum number of bytes to be written to MultiByteString. If this value causes the translated string to be truncated, RtlUnicodeToMultiByteN does not return an error status.

BytesInMultiByteString [out, optional]

Pointer to a caller-allocated variable that receives the length, in bytes, of the translated string. This parameter is optional and can be NULL.

UnicodeString [in]

Pointer to the Unicode source string to be translated.

BytesInUnicodeString [in]

Size, in bytes, of the string at UnicodeString.

Return value

RtlUnicodeToMultiByteN returns STATUS_SUCCESS.

Remarks

RtlUnicodeToMultiByteN translates the given Unicode string using the current system ANSI code page that was installed at system boot time.

Although BytesInMultiByteString is optional and can be NULL, callers should provide storage for it, because the received length can be used to determine whether the conversion was successful.

This routine does not modify the source string. It returns a null-terminated multibyte string if the given BytesInUnicodeString included a NULL terminator and if the given MaxBytesInMultiByteString did not cause truncation.

Like RtlUnicodeToMultiByteSize, RtlUnicodeToMultiByteN supports only precomposed Unicode characters that are mapped to the current system ANSI code page installed at system boot.

For information about other string-handling routines, see Run-Time Library (RTL) Routines.

See also

RtlMultiByteToUnicodeN

RtlUnicodeToMultiByteSize

RtlUpcaseUnicodeToMultiByteN

View the official Windows Driver Kit DDI reference

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