StringCbCatNExA function (strsafe.h)

Concatenates the specified number of bytes 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.

StringCbCatNEx is a replacement for the following functions:

• strncat
• StrNCat

StringCbCatNEx adds to the functionality of StringCbCatN by returning a pointer to the end of the destination string as well as the number of bytes left unused in that string. Flags may also be passed to the function for additional control.

Syntax

STRSAFEAPI StringCbCatNExA(
  [in, out]       STRSAFE_LPSTR  pszDest,
  [in]            size_t         cbDest,
  [in]            STRSAFE_PCNZCH pszSrc,
  [in]            size_t         cbToAppend,
  [out, optional] STRSAFE_LPSTR  *ppszDestEnd,
  [out, optional] size_t         *pcbRemaining,
  [in]            DWORD          dwFlags
);

Parameters

[in, out] pszDest

Type: LPTSTR

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 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 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).

[in] pszSrc

Type: LPCTSTR

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

[in] cbToAppend

Type: size_t

The maximum number of bytes to append to pszDest.

[out, optional] ppszDestEnd

Type: LPTSTR*

The address of a pointer to the end of pszDest. If ppszDestEnd is non-NULL and any data is appended to the destination buffer, this points to the terminating null character at the end of the string.

[out, optional] pcbRemaining

Type: size_t*

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.

[in] dwFlags

Type: DWORD

One or more of the following values.

Value	Meaning
STRSAFE_FILL_BEHIND_NULL 0x00000200	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 0x00000100	Treat NULL string pointers like empty strings (TEXT("")).
STRSAFE_FILL_ON_FAILURE 0x00000400	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 0x00000800	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 0x00001000	If the function fails, pszDest is untouched. Nothing is added to the original contents.

Return value

Type: HRESULT

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
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 may contain 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.

Remarks

Compared to the functions it replaces, 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 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 unless the STRSAFE_IGNORE_NULLS flag is specified, in which case both may be NULL. However, an error due to insufficient space may still be returned even though NULL values are ignored.

StringCbCatNEx 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"	StringCbCatNExA
TCHAR	TEXT("string")	StringCbCatNEx
WCHAR	L"string"	StringCbCatNExW

 

Requirements

Requirement	Value
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

Reference

StringCbCatEx

StringCbCatN

StringCchCatNEx