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

NTSTATUS
  RtlStringCbCatExW(
    IN OUT LPWSTR  pszDest  OPTIONAL,
    IN size_t  cbDest,
    IN LPCWSTR  pszSrc  OPTIONAL,
    OUT LPWSTR*  ppszDestEnd  OPTIONAL,
    OUT size_t*  pcbRemaining  OPTIONAL,
    IN DWORD  dwFlags
    );

NTSTATUS
  RtlStringCbCatExA(
    IN OUT LPSTR  pszDest  OPTIONAL,
    IN size_t  cbDest,
    IN LPCSTR  pszSrc  OPTIONAL,
    OUT LPSTR*  ppszDestEnd  OPTIONAL,
    OUT size_t*  pcbRemaining  OPTIONAL,
    IN DWORD  dwFlags
    );

Parameters

pszDest

Optional. Caller-supplied 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

Supplies 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

Optional. Caller-supplied 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

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

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

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

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.

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.

Comments

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.

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

IRQL: PASSIVE_LEVEL

Headers: Declared in Ntstrsafe.h. Include Ntstrsafe.h. Link to Ntstrsafe.lib.

See Also

RtlStringCbCat, RtlStringCchCatEx, RtlStringCbCatNEx