RtlUnicodeStringCatString function

The RtlUnicodeStringCatString function concatenates two strings when the destination string is contained in a UNICODE_STRING structure.


NTSTATUS RtlUnicodeStringCatString(
  _Inout_ PUNICODE_STRING  DestinationString,


DestinationString [in, out]

A pointer to a UNICODE_STRING structure. This structure includes a buffer that, on input, contains a destination string to which the source string will be concatenated. On output, this buffer is the destination buffer that contains the entire resultant string. The source string (excluding the terminating null) is added to the end of the destination string. The maximum number of bytes in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH * sizeof(WCHAR).

pszSrc [in]

A pointer to a null-terminated string. This string will be concatenated to the end of the string that is contained in the buffer that the UNICODE_STRING structure points to.

Return value

RtlUnicodeStringCatString returns one of the following NTSTATUS values.

Return codeDescription

This success status means that source data was present, the strings were concatenated without truncation, and the resultant destination buffer is null-terminated.


This warning status means that the concatenation operation did not complete because of insufficient buffer space. The destination buffer contains a truncated, null-terminated version of the intended result.


This error status means that the function received an invalid input parameter. For more information, see the following list.


RtlUnicodeStringCatString returns the STATUS_INVALID_PARAMETER value when one of the following occurs:

  • The contents of the UNICODE_STRING structure are invalid.
  • The destination buffer is already full.
  • A buffer pointer is NULL.
  • The destination buffer's length is zero, but a nonzero length source string is present.

For information about how to test NTSTATUS values, see Using NTSTATUS Values.


The RtlUnicodeStringCatString function uses the destination buffer's size to ensure that the concatenation operation does not write past the end of the buffer. The function does not terminate the resultant string with a null character value (that is, with zero).

If the source and destination strings overlap, the behavior of the function is undefined.

The pszSrc and DestinationString pointers cannot be NULL. If you need to handle NULL pointer values, use the RtlUnicodeStringCatStringEx function.

For more information about the safe string functions, see Using Safe String Functions.


Target platform



Available in Windows XP with Service Pack 1 (SP1) and later versions of Windows.


Ntstrsafe.h (include Ntstrsafe.h)





See also




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