StringCchCopyNA function (strsafe.h)

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

StringCchCopyN is a replacement for the following functions:


  [out] STRSAFE_LPSTR  pszDest,
  [in]  size_t         cchDest,
  [in]  STRSAFE_PCNZCH pszSrc,
  [in]  size_t         cchToCopy


[out] pszDest


The destination buffer, which receives the copied characters.

[in] cchDest

Type: size_t

The size of pszDest, in characters. This value must be large enough to hold the copied characters (the length of pszSrc or the value of cchSrc, whichever is smaller) plus 1 to account for the terminating null character. The maximum number of characters allowed is STRSAFE_MAX_CCH.

[in] pszSrc


The source string. This string must be readable up to cchSrc characters or a null terminator, whichever comes first.

[in] cchToCopy

Type: size_t

The maximum number of characters to be copied from pszSrc 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 characters were copied from pszSrc 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 copy 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.


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

While this routine is meant as a replacement for strncpy, there are differences in behavior. If cchSrc is larger than the number of characters in pszSrc, StringCchCopyN—unlike strncpy—does not continue to pad pszDest with null characters until cchSrc characters have been copied.

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

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

StringCchCopyN 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, as shown in the following table.

String Data Type String Literal Function
char "string" StringCchCopyNA
TCHAR TEXT("string") StringCchCopyN
WCHAR L"string" StringCchCopyNW


The strsafe.h header defines StringCchCopyN 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