StringCbCatNEx

Other versions of this page are also available for the following:

• Windows Embedded CE 6.0 R3

8/27/2008

This function is a replacement for strncat.

The size, in bytes, of the destination buffer is provided to the function to ensure that StringCbCatNEx does not write past the end of this buffer.

StringCbCatNEx adds to the functionality of StringCbCatN by returning a pointer to the end of the destination string, and by returning the number of bytes left unused in that string.

Flags can also be passed to the function for additional control.

Syntax

HRESULT StringCbCatNEx(      
    LPTSTR pszDest,
    size_t cbDest,
    LPCTSTR pszSrc,
    size_t cbMaxAppend,
    LPTSTR *ppszDestEnd,
    size_t *pcbRemaining,
    DWORD dwFlags
);

Parameters

• pszDest
  [in, out] Pointer to a buffer containing the string that pszSrc is concatenated to, and which contains the entire resultant string.

  The string at pszSrc is added to the end of the string at pszDest.

• cbDest
  [in] Size of the destination buffer, in bytes.

  This value must consider the length of pszSrc, plus the length of pszDest, plus the bytes used for the terminating null character.

  The maximum number of bytes allowed is STRSAFE_MAX_CCH * sizeof(TCHAR).

• pszSrc
  [in] Pointer to a buffer containing the source string that is concatenated to the end of pszDest.

  This source string must be null-terminated.

• cbMaxAppend
  [in] The maximum number of bytes to append to pszDest.

• p pszDestEnd
  [out] Address of a pointer to the end of pszDest.

  If ppszDestEnd is nonnull and data is appended to the destination buffer, this points to the terminating null character at the end of the string.

• pcbRemaining
  [out] Pointer to a variable that indicates the number of unused bytes in pszDest, including those used for the terminating null character.

  If pcbRemaining is NULL, the count is not kept or returned.

• dwFlags
  [in] One or more of the following values.

  Value	Description
  STRSAFE_FILL_BEHIND_NULL	If the function succeeds, the low byte of dwFlags (0) is used to fill the uninitialized portion of pszDest following the terminating null character.
  STRSAFE_IGNORE_NULLS	Treat null string pointers like empty strings (TEXT("")).
  STRSAFE_FILL_ON_FAILURE	If the function fails, the low byte of dwFlags (0) is used to fill the entire pszDest buffer, and the buffer is null-terminated. In the case of a STRSAFE_E_INSUFFICIENT_BUFFER failure, any pre-existing or truncated string in the destination buffer is overwritten.
  STRSAFE_NULL_ON_FAILURE	If the function fails, pszDest is set to an empty string (TEXT("")). In the case of a STRSAFE_E_INSUFFICIENT_BUFFER failure, any pre-existing or truncated string in the destination buffer is overwritten.
  STRSAFE_NO_TRUNCATION	If the function fails, pszDest is untouched. Nothing is added to the original contents.

Return Value

This function returns an HRESULT, as opposed to strncat, which returns a pointer.

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

Value	Description
S_OK	Source data was present, the strings were concatenated without truncation, and the resultant destination buffer is null-terminated.
STRSAFE_E_INVALID_PARAMETER	The value in cbDest is larger than STRSAFE_MAX_CCH * sizeof(TCHAR), an invalid flag was passed, or there are discrepancies between the size of the pszDest, cbDest, and the amount of material to append in pszSrc.
STRSAFE_E_INSUFFICIENT_BUFFER	The copy operation failed due to insufficient buffer space. Depending on the value of dwFlags, the destination buffer might contain a truncated, null-terminated version of the intended result. Where truncation is acceptable, this is not necessarily a failure condition.

Remarks

StringCbCatNEx provides additional processing for proper buffer handling in your code.

Poor buffer handling is implicated in many security issues that involve buffer overruns. StringCbCatNEx always null-terminates a nonzero-length destination buffer.

StringCbCatNEx can be used in its generic form, or specifically as StringCbCatNExA (for ANSI strings) or StringCbCatNExW (for Unicode strings). The form to use is determined by your data.

String data type	String literal	Function
char	"string"	StringCbCatNExA
TCHAR	TEXT("string")	StringCbCatNEx
WCHAR	L"string"	StringCbCatNExW

StringCbCatNEx and its ANSI and Unicode variants are replacements for these functions:

• strncat
• StrNCat

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

Neither pszSrc nor pszDest should be NULL unless the STRSAFE_IGNORE_NULLS flag is specified; in which case both might be NULL. However, an error due to insufficient space might still be returned even though null values are ignored.

Requirements

Header	strsafe.h
Windows Embedded CE	Windows CE 5.0 and later

See Also

Reference

StringCbCatN
StringCchCatNEx
StringCbCatEx