RtlStringCbCopyNW function (ntstrsafe.h)

Article
10/21/2021

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

Syntax

NTSTRSAFEDDI RtlStringCbCopyNW(
  [out] NTSTRSAFE_PWSTR pszDest,
  [in]  size_t          cbDest,
  [in]  STRSAFE_PCNZWCH pszSrc,
        size_t          cbToCopy
);

Parameters

[out] pszDest

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.

[in] cbDest

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).

[in] pszSrc

A pointer to a caller-supplied, null-terminated string.

cbToCopy

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.

Return code	Description
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 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.

Return code

Description

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 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.

Remarks

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.

String data type	String literal	Function
WCHAR	L"string"	RtlStringCbCopyNW
char	"string"	RtlStringCbCopyNA

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

Requirement	Value
Minimum supported client	Available in Windows XP with Service Pack 1 (SP1) and later versions of Windows.
Target Platform	Desktop
Header	ntstrsafe.h (include Ntstrsafe.h)
Library	Ntstrsafe.lib
IRQL	PASSIVE_LEVEL