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RtlStringCbCat function

The RtlStringCbCatW and RtlStringCbCatA functions concatenate two byte-counted strings.


NTSTATUS RtlStringCbCat(
  _Inout_  LPTSTR pszDest,
  _In_     size_t cbDest,
  _In_     LPCTSTR pszSrc


pszDest [in, out]

A pointer to a buffer which, on input, contains a null-terminated string to which pszSrc will be concatenated. On output, this is the destination buffer that contains the entire resultant string. The string at pszSrc is added to the end of the string at pszDest and terminated with a null character.

cbDest [in]

The size of the destination buffer, in bytes. The destination buffer must be large enough to include the concatenated strings and the terminating null character.

For Unicode strings, the maximum number of bytes is NTSTRSAFE_MAX_CCH * sizeof(WCHAR).

For ANSI strings, the maximum number of bytes is NTSTRSAFE_MAX_CCH * sizeof(char).

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 at pszDest.

Return value

The function returns one of the NTSTATUS values that are listed in the following table. For information about how to test NTSTATUS values, see Using NTSTATUS Values.

Return codeDescription

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


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


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

The STATUS_INVALID_PARAMETER return value means that one of the following occurred:

  • The value in cbDest is larger than the maximum buffer size.
  • The destination buffer was already full.
  • A NULL pointer was present.
  • The destination buffer length was zero, but a nonzero length source string was present.



RtlStringCbCatW and RtlStringCbCatA should be used instead of the following functions:

  • strcat

  • wcscat

Because RtlStringCbCatW and RtlStringCbCatA receive the size of the destination buffer as input, they will not write past the end of the buffer.

Use RtlStringCbCatW to handle Unicode strings and RtlStringCbCatA to handle ANSI strings. The form to use is determined by your data as shown in the following table.

String data typeString literalFunction








If pszSrc and pszDest point to strings that overlap, the behavior of the functions is undefined.

Neither pszSrc nor pszDest can be NULL. If you need to handle NULL string pointer values, use RtlStringCbCatNEx.

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



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


Ntstrsafe.h (include Ntstrsafe.h)





Unicode and ANSI names

RtlStringCbCatW (Unicode) and RtlStringCbCatA (ANSI)

See also




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