RtlUnicodeStringCchCatNEx function (ntstrsafe.h)
The RtlUnicodeStringCchCatNEx function concatenates two strings that are contained in UNICODE_STRING structures while limiting the size of the copied string.
Syntax
NTSTRSAFEDDI RtlUnicodeStringCchCatNEx(
[in, out] PUNICODE_STRING DestinationString,
[in] PCUNICODE_STRING SourceString,
[in] size_t cchToAppend,
[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 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 characters in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH. 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 characters in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH. SourceString can be NULL, but only if STRSAFE_IGNORE_NULLS is set in dwFlags.
[in] cchToAppend
The maximum number of characters to append to the string that the DestinationString parameter describes.
[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. RtlUnicodeStringCchCatNEx 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:
|
| 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
RtlUnicodeStringCchCatNEx 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 that the concatenated operation did not complete because of 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 that the function received an invalid input parameter. For more information, see the following list. |
RtlUnicodeStringCchCatNEx returns the STATUS_INVALID_PARAMETER value when:
- 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 in dwFlags.
- 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.
- The cchToAppend parameter's value is greater than NTSTRSAFE_UNICODE_STRING_MAX_CCH.
For information about how to test NTSTATUS values, see Using NTSTATUS Values.
Remarks
The RtlUnicodeStringCchCatNEx 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.
RtlUnicodeStringCchCatNEx adds to the functionality of the RtlUnicodeStringCchCatN 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 RtlUnicodeStringCchCatNEx 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 can be NULL. If the DestinationString pointer is NULL, the SourceString pointer must be NULL or the UNICODE_STRING structure must specify 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 |