StringCbCatNA function (strsafe.h)

Concatenates the specified number of bytes from one string to another string. The size, in bytes, of the destination buffer is provided to the function to ensure that it does not write past the end of this buffer.

StringCbCatN is a replacement for the following functions:


  [in, out] STRSAFE_LPSTR  pszDest,
  [in]      size_t         cbDest,
  [in]      STRSAFE_PCNZCH pszSrc,
  [in]      size_t         cbToAppend


[in, out] pszDest


The destination buffer, which contains the string that is to be concatenated to pszSrc, and will receive the resultant string. The string at pszSrc, up to cbMaxAppend bytes, is added to the end of the string at pszDest.

[in] cbDest

Type: size_t

The size of the destination buffer, in bytes. This value must consider the length of pszSrc plus either the length of pszDest or cbMaxAppend (whichever is smaller) plus the terminating null character. The maximum number of bytes allowed is STRSAFE_MAX_CCH * sizeof(TCHAR).

[in] pszSrc


The source string that is to be concatenated to the end of pszDest. This source string must be null-terminated.

[in] cbToAppend

Type: size_t

The maximum number of bytes to be appended to pszDest.

Return value


This function can return one of the following values. It is strongly recommended that you use the SUCCEEDED and FAILED macros to test the return value of this function.

Return code Description
Source data was present, the strings were concatenated without truncation, and the resultant destination buffer is null-terminated.
The value in cbDest is larger than the maximum allowed value, or the destination buffer is already full.
The concatenation operation failed due to insufficient buffer space. The destination buffer contains a truncated, null-terminated version of the intended result. In situations where truncation is acceptable, this may not necessarily be seen as a failure condition.

Note that this function returns an HRESULT value, unlike the functions that it replaces.


Compared to the functions it replaces, StringCbCatN provides additional processing for proper buffer handling in your code. Poor buffer handling is implicated in many security issues that involve buffer overruns. StringCbCatN always null-terminates and never overflows a valid destination buffer, even if the contents of the source string change during the operation.

Behavior is undefined if the strings pointed to by pszSrc and pszDest overlap.

Neither pszSrc nor pszDest should be NULL. See StringCbCatNEx if you require the handling of null string pointer values.

StringCbCatN can be used in its generic form, or in its more specific forms. The data type of the string determines the form of this function that you should use.

String Data Type String Literal Function
char "string" StringCbCatNA
TCHAR TEXT("string") StringCbCatN
WCHAR L"string" StringCbCatNW


The strsafe.h header defines StringCbCatN as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.


Minimum supported client Windows XP with SP2 [desktop apps | UWP apps]
Minimum supported server Windows Server 2003 with SP1 [desktop apps | UWP apps]
Target Platform Windows
Header strsafe.h

See also