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StringCchCatN function

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

StringCchCatN is a replacement for the following functions:


HRESULT StringCchCatN(
  _Inout_ LPTSTR  pszDest,
  _In_    size_t  cchDest,
  _In_    LPCTSTR pszSrc,
  _In_    size_t  cchMaxAppend


pszDest [in, out]


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

cchDest [in]

Type: size_t

The size of the destination buffer, in characters. This value must equal the length of pszSrc plus either the length of pszDest or cchMaxAppend (whichever is smaller). To this sum add 1 to account for the terminating null character. The maximum number of characters allowed is STRSAFE_MAX_CCH.

pszSrc [in]


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

cchMaxAppend [in]

Type: size_t

The maximum number of characters 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 codeDescription

Source data was present, the strings were concatenated without truncation, and the resultant destination buffer is null-terminated.


The value in cchDest is either larger than STRSAFE_MAX_CCH, 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, StringCchCatN provides additional processing for proper buffer handling in your code. Poor buffer handling is implicated in many security issues that involve buffer overruns. StringCchCatN 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 StringCchCatNEx if you require the handling of null string pointer values.

StringCchCatN 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 TypeString LiteralFunction



Minimum supported client

Windows XP with SP2 [desktop apps | Windows Store apps]

Minimum supported server

Windows Server 2003 with SP1 [desktop apps | Windows Store apps]



Unicode and ANSI names

StringCchCatNW (Unicode) and StringCchCatNA (ANSI)

See also




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