The RtlStringCbCopyNW and RtlStringCbCopyNA functions copy a byte-counted string to a buffer while limiting the size of the copied string.

NTSTATUS
  RtlStringCbCopyNW(
    OUT LPWSTR  pszDest,
    IN size_t  cbDest,
    IN LPCWSTR  pszSrc,
    IN size_t  cbSrc
    );

NTSTATUS
  RtlStringCbCopyNA(
    OUT LPSTR  pszDest,
    IN size_t  cbDest,
    IN LPCSTR  pszSrc,
    IN size_t  cbSrc
    );

Parameters

pszDest

Supplies a pointer to a caller-supplied buffer that receives the copied string. The string at pszSrc, up to cbSrc bytes, is copied to the buffer at pszDest and terminated with a NULL character.

cbDest

Supplies the size, in bytes, of the destination buffer. The buffer must be large enough for both the string 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

Supplies a pointer to a caller-supplied, NULL-terminated string.

cbSrc

Supplies the maximum number of bytes to copy from pszSrc to 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.

The function returns the STATUS_INVALID_PARAMETER value when:

• The value in cbDest 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

RtlStringCbCopyNW and RtlStringCbCopyNA should be used instead of strncpy. However, these functions differ in behavior. If cbSrc is larger than the number of bytes in pszSrc, the RtlStringCbCopyN functions—unlike strncpy—do not fill pszDest with NULL characters until cbSrc bytes have been copied.

RtlStringCbCopyN copies a given number of bytes from a source string. The size, in bytes, of the destination buffer is provided to the function to ensure that RtlStringCbCopyN does not write past the end of this buffer.

Use RtlStringCbCopyNW to handle Unicode strings and RtlStringCbCopyNA to handle ANSI strings. The form you use depends on 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. If you need to handle null string pointer values, see RtlStringCbCopyNEx.

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

RtlStringCbCopy, RtlStringCchCopyN, RtlStringCbCopyNEx