RtlStringCchCopyNW function (ntstrsafe.h)

Article
10/21/2021

The RtlStringCchCopyNW and RtlStringCchCopyNA functions copy a character-counted string to a buffer while limiting the size of the copied string.

Syntax

NTSTRSAFEDDI RtlStringCchCopyNW(
  [out] NTSTRSAFE_PWSTR pszDest,
  [in]  size_t          cchDest,
  [in]  STRSAFE_PCNZWCH pszSrc,
        size_t          cchToCopy
);

Parameters

[out] pszDest

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.

[in] cchDest

The size of the destination buffer, in characters. The maximum number of characters allowed is NTSTRSAFE_MAX_CCH.

[in] pszSrc

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

cchToCopy

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 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 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.

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 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.

Remarks

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

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	Any if strings being manipulated are always resident in memory, otherwise PASSIVE_LEVEL