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RtlStringCbPrintf function

The RtlStringCbPrintfW and RtlStringCbPrintfA functions create a byte-counted text string, with formatting that is based on supplied formatting information.


NTSTATUS RtlStringCbPrintf(
  _Out_ LPTSTR  pszDest,
  _In_  size_t  cbDest,
  _In_  LPCTSTR pszFormat,


pszDest [out]

A pointer to a caller-supplied buffer that receives a formatted, null-terminated string. The function creates this string from both the formatting string that is supplied by pszFormat and the function's argument list.

cbDest [in]

The size of the destination buffer, in bytes. The buffer must be large enough to contain the formatted string plus 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).

pszFormat [in]

A pointer to a null-terminated text string that contains printf-styled formatting directives.


A list of arguments that are interpreted by the function based on formatting directives contained in the pszFormat 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 codeDescription

This success status means source data was present, the string was created without truncation, and the resultant destination buffer is null-terminated.


This warning status means the operation did not complete due to insufficient space in the destination buffer. The destination buffer contains a truncated version of the output string.


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.



RtlStringCbPrintfW and RtlStringCbPrintfA should be used instead of the following functions:

  • sprintf

  • swprintf

  • _snprintf

  • _snwprintf

All of these functions accept a format string and a list of arguments, interpret them, and create a formatted string. The size, in bytes, of the destination buffer is provided to RtlStringCbPrintfW and RtlStringCbPrintfA to ensure that they do not write past the end of the buffer.

Use RtlStringCbPrintfW to handle Unicode strings and RtlStringCbPrintfA to handle ANSI strings. The form you use depends on your data, as shown in the following table.

String data typeString literalFunction








If pszDest and pszFormat point to overlapping string or if any argument strings overlap, the behavior of the function is undefined.

Neither pszFormat nor pszDest can be NULL. If you need to handle NULL string pointer values, use RtlStringCbPrintfEx.

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


The following example shows a basic use of RtlStringCbPrintfW using four arguments.

int const arraysize = 30;
WCHAR pszDest[arraysize]; 
size_t cbDest = arraysize * sizeof(WCHAR);

LPCWSTR pszFormat = L"%s %d + %d = %d.";
WCHAR* pszTxt = L"The answer is";

NTSTATUS status = RtlStringCbPrintfW(pszDest, cbDest, pszFormat, pszTxt, 1, 2, 3);

The resultant string is "The answer is 1 + 2 = 3." It is contained in the buffer at pszDest.


Target platform



Available starting with Windows XP with Service Pack 1 (SP1).


Ntstrsafe.h (include Ntstrsafe.h)





Unicode and ANSI names

RtlStringCbPrintfW (Unicode) and RtlStringCbPrintfA (ANSI)

See also




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