StringCchCatNEx 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.

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

StringCchCatNEx is a replacement for the following functions:

• strncat
• StrNCat

Syntax

HRESULT StringCchCatNEx(
  _Inout_   LPTSTR  pszDest,
  _In_      size_t  cchDest,
  _In_      LPCTSTR pszSrc,
  _In_      size_t  cchMaxAppend,
  _Out_opt_ LPTSTR  *ppszDestEnd,
  _Out_opt_ size_t  *pcchRemaining,
  _In_      DWORD   dwFlags
);

Parameters

pszDest [in, out]

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.

cchDest [in]

Type: size_t

The size of the destination buffer, in characters. This value must equal the length of pszSrc plus the length of pszDest plus 1 to account for the terminating null character. The maximum number of characters allowed is STRSAFE_MAX_CCH.

pszSrc [in]

Type: LPCTSTR

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.

ppszDestEnd [out, optional]

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.

pcchRemaining [out, optional]

Type: size_t*

The number of unused characters in pszDest, including the terminating null character. If pcchRemaining is NULL, the count is not kept or returned.

dwFlags [in]

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.

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

Remarks

Compared to the functions it replaces, StringCchCatNEx provides additional processing for proper buffer handling in your code. Poor buffer handling is implicated in many security issues that involve buffer overruns. StringCchCatNEx 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.

StringCchCatNEx 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.

Requirements

See also

Reference

StringCchCatN

StringCbCatNEx

StringCchCatEx