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RtlStringCchCatNExW function (ntstrsafe.h)

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The RtlStringCchCatNExW and RtlStringCchCatNExA functions concatenate two character-counted strings while limiting the size of the appended string.

Syntax

NTSTRSAFEDDI RtlStringCchCatNExW(
  [in, out, optional] NTSTRSAFE_PWSTR pszDest,
  [in]                size_t          cchDest,
  [in, optional]      STRSAFE_PCNZWCH pszSrc,
                      size_t          cchToAppend,
  [out, optional]     NTSTRSAFE_PWSTR *ppszDestEnd,
  [out, optional]     size_t          *pcchRemaining,
  [in]                DWORD           dwFlags
);

Parameters

[in, out, optional] pszDest

A pointer to a buffer which, on input, contains a null-terminated string to which pszSrc will be concatenated. On output, this is the destination buffer that contains the entire resultant string. The string at pszSrc, up to cchMaxAppend characters, is added to the end of the string at pszDest and terminated with a null character. The pszDest pointer can be NULL, but only if STRSAFE_IGNORE_NULLS is set in dwFlags.

[in] cchDest

The size of the destination buffer, in characters. The maximum number of characters allowed is NTSTRSAFE_MAX_CCH. If pszDest is NULL, cchDest must be zero.

[in, optional] pszSrc

A pointer to a null-terminated string. This string will be concatenated to the end of the string that is contained in the buffer at pszDest. The pszSrc pointer can be NULL, but only if STRSAFE_IGNORE_NULLS is set in dwFlags.

cchToAppend

The maximum number of characters to append to the string that is contained in the buffer at pszDest.

[out, optional] ppszDestEnd

If the caller supplies a non-NULL address pointer, then after the concatenation operation completes, the function loads that address with a pointer to the destination buffer's resulting null string terminator.

[out, optional] pcchRemaining

If the caller supplies a non-NULL address pointer, the function loads the address with the number of unused characters in the buffer pointed to by pszDest, including the terminating null character.

[in] dwFlags

One or more flags and, optionally, a fill byte. The flags are defined as follows:

Value Meaning
STRSAFE_FILL_BEHIND_NULL If this flag is set and the function succeeds, the low byte of dwFlags is used to fill the portion of the destination buffer that follows the terminating null character.
STRSAFE_IGNORE_NULLS If this flag is set, either pszDest or pszSrc, or both, can be NULL. NULL pszSrc pointers are treated like empty strings (TEXT("")), which can be copied. NULL pszDest pointers cannot receive nonempty strings.
STRSAFE_FILL_ON_FAILURE If this flag is set and the function fails, the low byte of dwFlags is used to fill the entire destination buffer, and the buffer is null-terminated. This operation overwrites any preexisting buffer contents.
STRSAFE_NULL_ON_FAILURE If this flag is set and the function fails, the destination buffer is set to an empty string (TEXT("")). This operation overwrites any preexisting buffer contents.
STRSAFE_NO_TRUNCATION

If this flag is set and the function returns STATUS_BUFFER_OVERFLOW:

  • If STRSAFE_FILL_ON_FAILURE is also specified, STRSAFE_NO_TRUNCATION fills the destination buffer accordingly.
  • Otherwise, the destination buffer will be unmodified.

Return value

The function returns one of the NTSTATUS values that are listed in the following table. For information about how to test NTSTATUS values, see Using NTSTATUS Values.

Return code Description
STATUS_SUCCESS This success status means source data was present, the output string was created without truncation, and the resultant destination buffer is null-terminated.
STATUS_BUFFER_OVERFLOW This warning status means the operation did not complete due to insufficient space in the destination buffer. If STRSAFE_NO_TRUNCATION is set, see the dwFlags parameter for more information.
STATUS_INVALID_PARAMETER

This error status means the function received an invalid input parameter. For more information, see the following paragraph.

The function returns the STATUS_INVALID_PARAMETER value when:

  • An invalid flag was specified.
  • The value in cchDest is larger than the maximum buffer size.
  • The destination buffer was already full.
  • A NULL pointer was present without the STRSAFE_IGNORE_NULLS flag.
  • The destination buffer pointer was NULL, but the buffer size was not zero.
  • The destination buffer pointer was NULL, or its length was zero, but a nonzero length source string was present.

Remarks

RtlStringCchCatNExW and RtlStringCchCatNExA should be used instead of the following functions:

  • strncat
  • wcsncat

The size, in characters, of the destination buffer is provided to RtlStringCchCatNExW and RtlStringCchCatNExA to ensure that the functions do not write past the end of the buffer.

RtlStringCchCatNExW and RtlStringCchCatNExA add to the functionality of RtlStringCchCatN by returning a pointer to the end of the destination string, as well as the number of characters left unused in that string. Flags can be passed to the function for additional control.

Use RtlStringCchCatNExW to handle Unicode strings and RtlStringCchCatNExA to handle ANSI strings. The form you use depends on your data, as shown in the following table.

String data type String literal Function
WCHAR L"string" RtlStringCchCatNExW
char "string" RtlStringCchCatNExA

If pszSrc and pszDest point to overlapping strings, the behavior of the function is undefined.

Neither pszSrc nor pszDest can be NULL unless the STRSAFE_IGNORE_NULLS flag is set, in which case either or both can be NULL. If pszDest is NULL, pszSrc must either be NULL or point to an empty string.

For more information about the safe string functions, see Using safe string functions.

Requirements

Requirement Value
Minimum supported client Available in Windows XP with Service Pack 1 (SP1) and later versions of Windows.
Target Platform Desktop
Header ntstrsafe.h (include Ntstrsafe.h)
Library Ntstrsafe.lib
IRQL Any if strings being manipulated are always resident in memory, otherwise PASSIVE_LEVEL

See also