RtlStringCchCatA function

The RtlStringCchCatW and RtlStringCchCatA functions concatenate two character-counted strings.


  size_t          cchDest,



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.


The size, in characters, of the destination buffer. The maximum number of characters allowed is NTSTRSAFE_MAX_CCH.


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 code Description
This success status means source data was present, the output string was created without truncation, and the resultant destination buffer is null-terminated.
This warning status means the operation did not complete due to insufficient space in the destination buffer. 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 function returns the STATUS_INVALID_PARAMETER value when:
  • The value in cchDest is larger than the maximum buffer size.
  • The destination buffer was already full.
  • A NULL pointer was present.
  • The destination buffer pointer was NULL, but the buffer size was not zero.
  • The destination buffer length was zero, but a nonzero length source string was present.


RtlStringCchCatW and RtlStringCchCatA should be used instead of the following functions:

  • strcat

  • wcscat

The size, in characters, of the destination buffer is provided to ensure that RtlStringCchCatW and RtlStringCchCatA do not write past the end of the buffer.

Use RtlStringCchCatW to handle Unicode strings and RtlStringCchCatA to handle ANSI strings. The form you use depends on your data, as shown in the following table.

String data type String literal Function
WCHAR L"string" RtlStringCchCatW
char "string" RtlStringCchCatA

If pszSrc and pszDest point to overlapping strings, the behavior of the function is undefined.

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

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


Windows version Available in Windows XP with Service Pack 1 (SP1) and later versions of Windows.
Target Platform Desktop
Header ntstrsafe.h (include Ntstrsafe.h)
Library Ntstrsafe.lib

See Also