StringCchVPrintfExA function (strsafe.h)

Writes formatted data to the specified string using a pointer to a list of arguments. The size of the destination buffer is provided to the function to ensure that it does not write past the end of this buffer.

StringCchVPrintfEx adds to the functionality of StringCchVPrintf by returning a pointer to the end of the destination string as well as the number of characters left unused in that string. Flags may also be passed to the function for additional control.

StringCchVPrintfEx is a replacement for the following functions:

• vsprintf, vswprintf, _vstprintf
• vsnprintf, _vsnwprintf, _vsntprintf
• wvsprintf
• wvnsprintf

Syntax

STRSAFEAPI StringCchVPrintfExA(
  [out]           STRSAFE_LPSTR  pszDest,
  [in]            size_t         cchDest,
  [out, optional] STRSAFE_LPSTR  *ppszDestEnd,
  [out, optional] size_t         *pcchRemaining,
  [in]            DWORD          dwFlags,
  [in]            STRSAFE_LPCSTR pszFormat,
  [in]            va_list        argList
);

Parameters

[out] pszDest

Type: LPTSTR

The destination buffer, which receives the formatted, null-terminated string created from pszFormat and argList.

[in] cchDest

Type: size_t

The size of the destination buffer, in characters. This value must be sufficiently large to accommodate the final formatted string plus 1 to account for the terminating null character. The maximum number of characters allowed is STRSAFE_MAX_CCH.

[out, optional] ppszDestEnd

Type: LPTSTR*

The address of a pointer to the end of pszDest. If ppszDestEnd is non-NULL and any data is copied into the destination buffer, this points to the terminating null character at the end of the string.

[out, optional] pcchRemaining

Type: size_t*

The number of unused characters in pszDest, including the terminating null character. If pcchRemaining is NULL, the count is not kept or returned.

[in] dwFlags

Type: DWORD

One or more of the following values.

Value	Meaning
STRSAFE_FILL_BEHIND_NULL 0x00000200	If the function succeeds, the low byte of dwFlags (0) is used to fill the uninitialized portion of pszDest following the terminating null character.
STRSAFE_IGNORE_NULLS 0x00000100	Treat NULL string pointers like empty strings (TEXT("")).
STRSAFE_FILL_ON_FAILURE 0x00000400	If the function fails, the low byte of dwFlags (0) is used to fill the entire pszDest buffer, and the buffer is null-terminated. In the case of a STRSAFE_E_INSUFFICIENT_BUFFER failure, any truncated string returned is overwritten.
STRSAFE_NULL_ON_FAILURE 0x00000800	If the function fails, pszDest is set to an empty string (TEXT("")). In the case of a STRSAFE_E_INSUFFICIENT_BUFFER failure, any truncated string is overwritten.
STRSAFE_NO_TRUNCATION 0x00001000	As in the case of STRSAFE_NULL_ON_FAILURE, if the function fails, pszDest is set to an empty string (TEXT("")). In the case of a STRSAFE_E_INSUFFICIENT_BUFFER failure, any truncated string is overwritten.

[in] pszFormat

Type: LPCTSTR

The format string. This string must be null-terminated. For more information, see Format Specification Syntax.

[in] argList

Type: va_list

The arguments to be inserted into the pszFormat string.

Return value

Type: HRESULT

This function can return one of the following values. It is strongly recommended that you use the SUCCEEDED and FAILED macros to test the return value of this function.

Return code	Description
S_OK	There was sufficient space for the result to be copied to pszDest without truncation and the buffer is null-terminated.
STRSAFE_E_INVALID_PARAMETER	The value in cchDest is either 0 or larger than STRSAFE_MAX_CCH, or the destination buffer is already full.
STRSAFE_E_INSUFFICIENT_BUFFER	The copy operation failed due to insufficient buffer space. Depending on the value of dwFlags, the destination buffer may contain a truncated, null-terminated version of the intended result. In situations where truncation is acceptable, this may not necessarily be seen as a failure condition.

 

Note that this function returns an HRESULT value, unlike the functions that it replaces.

Remarks

StringCchVPrintfEx provides additional processing for proper buffer handling in your code. Poor buffer handling is implicated in many security issues that involve buffer overruns. StringCchVPrintfEx always null-terminates a nonzero-length destination buffer.

For more information on va_lists, see the conventions defined in Stdarg.h.

Behavior is undefined if the strings pointed to by pszDest, pszFormat, or any argument strings overlap.

Neither pszFormat nor pszDest should be NULL unless the STRSAFE_IGNORE_NULLS flag is specified, in which case both may be NULL. However, an error due to insufficient space may still be returned even though NULL values are ignored.

StringCchVPrintfEx can be used in its generic form, or in its more specific forms. The data type of the string determines the form of this function that you should use, as shown in the following table.

String Data Type	String Literal	Function
char	"string"	StringCchVPrintfExA
TCHAR	TEXT("string")	StringCchVPrintfEx
WCHAR	L"string"	StringCchVPrintfExW

 

Note

The strsafe.h header defines StringCchVPrintfEx as an alias that automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that is not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

Requirement	Value
Minimum supported client	Windows XP with SP2 [desktop apps | UWP apps]
Minimum supported server	Windows Server 2003 with SP1 [desktop apps | UWP apps]
Target Platform	Windows
Header	strsafe.h

See also

Reference

StringCbVPrintfEx

StringCchPrintfEx

StringCchVPrintf