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RtlStringCbCatEx function

The RtlStringCbCatExW and RtlStringCbCatExA functions concatenate two byte-counted strings.

Syntax


NTSTATUS RtlStringCbCatEx(
  _Inout_opt_  LPTSTR pszDest,
  _In_         size_t cbDest,
  _In_opt_     LPCTSTR pszSrc,
  _Out_opt_    LPTSTR *ppszDestEnd,
  _Out_opt_    size_t *pcbRemaining,
  _In_         DWORD dwFlags
);

Parameters

pszDest [in, out, optional]

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 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.

cbDest [in]

The size of the destination buffer, in bytes. The buffer must be large enough to include both strings and the terminating null character.

For Unicode strings, the maximum number of bytes is NTSTRSAFE_MAX_CCH * sizeof(WCHAR).

For ANSI strings, the maximum number of bytes is NTSTRSAFE_MAX_CCH * sizeof(char).

pszSrc [in, optional]

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.

ppszDestEnd [out, optional]

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.

pcbRemaining [out, optional]

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

dwFlags [in]

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

ValueMeaning
STRSAFE_FILL_BEHIND_NULL

If 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 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 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 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 set and the function returns STATUS_BUFFER_OVERFLOW, the contents of the destination buffer are not modified.

 

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 codeDescription
STATUS_SUCCESS

This success status means source data was present, the strings were fully concatenated without truncation, and the resultant destination buffer is null-terminated.

STATUS_BUFFER_OVERFLOW

This warning status means the copy operation did not complete due to insufficient space in the destination buffer. If STRSAFE_NO_TRUNCATION is set in dwFlags, the destination buffer is not modified. If the flag is not set, the destination buffer contains a truncated version of the concatenated string.

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 when:

  • An invalid flag was specified.
  • The value in cbDest 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

RtlStringCbCatExW and RtlStringCbCatExA should be used instead of the following functions:

  • strcat

  • wcscat

Because RtlStringCbCatExW and RtlStringCbCatExA receive the size of the destination buffer as input, they will not write past the end of the buffer.

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

Use RtlStringCbCatExW to handle Unicode strings and RtlStringCbCatExA to handle ANSI strings. The form to use is determined by your data, as shown in the following table.

String data typeString literalFunction

WCHAR

L"string"

RtlStringCbCatExW

char

"string"

RtlStringCbCatExA

 

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

Version

Available in Windows XP with Service Pack 1 (SP1) and later versions of Windows.

Header

Ntstrsafe.h (include Ntstrsafe.h)

Library

Ntstrsafe.lib

IRQL

PASSIVE_LEVEL

Unicode and ANSI names

RtlStringCbCatExW (Unicode) and RtlStringCbCatExA (ANSI)

See also

RtlStringCbCat
RtlStringCchCatEx
RtlStringCbCatNEx

 

 

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