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RtlUnicodeStringCatEx function (ntstrsafe.h)

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The RtlUnicodeStringCatEx function concatenates two strings that are contained in UNICODE_STRING structures.

Syntax

NTSTRSAFEDDI RtlUnicodeStringCatEx(
  [in, out]       PUNICODE_STRING  DestinationString,
  [in]            PCUNICODE_STRING SourceString,
  [out, optional] PUNICODE_STRING  RemainingString,
  [in]            DWORD            dwFlags
);

Parameters

[in, out] DestinationString

Optional. A pointer to a UNICODE_STRING structure. This structure includes a buffer that, on input, contains a destination string to which the source string will be concatenated. On output, this buffer is the destination buffer that contains the entire resultant string. The source string is added to the end of the destination string. The maximum number of bytes in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH * sizeof(WCHAR). DestinationString can be NULL, but only if STRSAFE_IGNORE_NULLS is set in dwFlags.

[in] SourceString

Optional. A pointer to a UNICODE_STRING structure. This structure includes a buffer that contains the source string. This string will be added to the end of the destination string. The maximum number of bytes in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH * sizeof(WCHAR). SourceString can be NULL, but only if STRSAFE_IGNORE_NULLS is set in dwFlags.

[out, optional] RemainingString

Optional. If the caller supplies a non-NULL pointer to a UNICODE_STRING structure, the function sets this structure's Buffer member to the end of the concatenated string, sets the structure's Length member to zero, and sets the structure's MaximumLength member to the number of bytes that are remaining in the destination buffer. RemainingString can be NULL, but only if STRSAFE_IGNORE_NULLS is set in dwFlags.

[in] dwFlags

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

Value Meaning
STRSAFE_FILL_BEHIND 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 last character in the string.
STRSAFE_IGNORE_NULLS If this flag is set, the source or destination pointer, or both, can be NULL. RtlUnicodeStringCatEx treats NULL source buffer pointers like empty strings (TEXT("")), which can be copied. NULL destination buffer 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. 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.
STRSAFE_ZERO_LENGTH_ON_FAILURE If this flag is set and the function returns STATUS_BUFFER_OVERFLOW, the destination string length is set to zero bytes.

Return value

RtlUnicodeStringCatEx returns one of the following NTSTATUS values.

Return code Description
STATUS_SUCCESS This success status means source data was present, and the strings were concatenated without truncation.
STATUS_BUFFER_OVERFLOW This warning status means the concatenation 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 list.

RtlUnicodeStringCatEx returns the STATUS_INVALID_PARAMETER value when one of the following occurs:

  • The contents of a UNICODE_STRING structure are invalid.
  • An invalid flag is specified in dwFlags.
  • The destination buffer is already full.
  • A buffer pointer is NULL and the STRSAFE_IGNORE_NULLS flag is not specified.
  • The destination buffer pointer is NULL, but the buffer size is not zero.
  • The destination buffer pointer is NULL, or its length is zero, but a nonzero length source string is present.

For information about how to test NTSTATUS values, see Using NTSTATUS Values.

Remarks

The RtlUnicodeStringCatEx function uses the destination buffer's size to ensure that the concatenation operation does not write past the end of the buffer. By default, the function does not terminate the resultant string with a null character value (that is, with zero). As an option, the caller can use the STRSAFE_FILL_BEHIND flag and a fill byte value of zero to null-terminate a resultant string that does not occupy the entire destination buffer.

RtlUnicodeStringCatEx adds to the functionality of the RtlUnicodeStringCat function by returning a UNICODE_STRING structure that identifies the end of the destination string and the number of bytes that are left unused in that string. You can pass flags to RtlUnicodeStringCatEx for additional control.

If the source and destination strings overlap, the behavior of the function is undefined.

The SourceString and DestinationString pointers cannot be NULL unless the STRSAFE_IGNORE_NULLS flag is set in dwFlags. If STRSAFE_IGNORE_NULLS is set, one or both of these pointers can be NULL. If the DestinationString pointer is NULL, the SourceString pointer must be NULL or the UNICODE_STRING structure must describe an empty string.

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

Requirements

Requirement Value
Minimum supported client Available starting with Windows XP with Service Pack 1 (SP1).
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