Windows Driver Kit: Kernel-Mode Driver Architecture
RtlStringCchCopyN
The RtlStringCchCopyNW and RtlStringCchCopyNA functions copy a character-counted string to a buffer while limiting the size of the copied string.
NTSTATUS
RtlStringCchCopyNW(
OUT LPWSTR pszDest,
IN size_t cchDest,
IN LPCWSTR pszSrc,
IN size_t cchSrc
);
NTSTATUS
RtlStringCchCopyNA(
OUT LPSTR pszDest,
IN size_t cchDest,
IN LPCSTR pszSrc,
IN size_t cchSrc
);
Parameters
- pszDest
- Supplies a pointer to a caller-supplied buffer that receives the copied string. The string at pszSrc, up to cchSrc characters, is copied to the buffer at pszDest and terminated with a NULL character.
- cchDest
- Supplies the size of the destination buffer, in characters. The maximum number of characters allowed is NTSTRSAFE_MAX_CCH.
- pszSrc
- Supplies a pointer to a caller-supplied, null-terminated string.
- cchSrc
- Supplies the maximum number of characters to copy from pszSrc to the buffer that is supplied by pszDest.
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 value | Meaning |
|---|
| STATUS_SUCCESS | This success status means source data was present, the string was copied 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. The destination buffer contains a truncated version of the copied 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 value when:
- The value in cchDest is larger than the maximum buffer size.
- The destination buffer was already full.
- A NULL pointer was present.
- The destination buffer's length was zero, but a nonzero length source string was present.
Comments
RtlStringCchCopyNW and RtlStringCchCopyNA should be used instead of strncpy.
The functions copy a given number of characters from a source string. RtlStringCchCopyNW and RtlStringCchCopyNA receive the size, in characters, of the destination buffer to ensure that the functions do not write past the end of the buffer.
Note that these functions behave differently from strncpy in one respect. If cchSrc is larger than the number of characters in pszSrc, RtlStringCchCopyNW and RtlStringCchCopyNA —unlike strncpy—do not continue to pad pszDest with NULL characters until cchSrc characters have been copied.
Use RtlStringCchCopyNW to handle Unicode strings and RtlStringCchCopyNA 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" | RtlStringCchCopyNW |
| char | "string" | RtlStringCchCopyNA |
If pszSrc and pszDest point to overlapping strings, the behavior of the function is undefined.
Neither pszSrc nor pszDest can be NULL. If you need to handle null string pointer values, use RtlStringCchCopyNEx.
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
RtlStringCbCopyN, RtlStringCchCopy, RtlStringCchCopyNEx