RtlStringCbCopyA function

The RtlStringCbCopyW and RtlStringCbCopyA functions copy a byte-counted string into a buffer.


  size_t          cbDest,



A pointer to a caller-supplied buffer that receives the copied string. The string at pszSrc is copied to the buffer at pszDest and terminated with a null character.


The size, in bytes, of the destination buffer. The buffer must be large enough for 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).


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

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
This success status means source data was present, the string was copied without truncation, and the resultant destination buffer is null-terminated.
This warning status means the copy operation did not complete due to insufficient buffer space. The destination buffer contains a truncated, null-terminated version of the intended result.
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.


RtlStringCbCopyA and RtlStringCbCopyW should be used instead of the following functions:

  • strcpy

  • wcscpy

RtlStringCbCopyA and RtlStringCbCopyW are not replacements for strncpy. To replace strncpy, use RtlStringCbCopyN or RtlStringCbCopyNEx.

The size of the destination buffer is provided to the function to ensure that RtlStringCbCopy does not write past the end of the buffer.

Use RtlStringCbCopyW to handle Unicode strings and RtlStringCbCopyA 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" RtlStringCbCopyW
char "string" RtlStringCbCopyA

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 RtlStringCbCopyEx.

For more information about the safe string functions, see Using Safe String Functions.


Windows version 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

See Also